Using Cement to make Live Rock in Creative Shapes.
An excellent alternative is to make cement reef
rocks in your own choice of interesting shapes and sizes. Please
read and follow the simple, proper and vital pH curing and testing procedures
listed below if you make cement reef rocks. Making
and using cement rock for aquariums is nothing new. Public aquariums and
aquarists in the United States and Europe used cement long ago. Dick Perrin of
Tropicorium has used cement in the past for culturing live rock. About a decade
ago he started making cement rocks to grow into live rocks for sale. He now uses
mostly CaribSea's Reef Rocks when growing aquacultured live rocks. Using cement
to make creatively shaped rocks for reef aquariums is a lost art of sorts that
is being revived and developed even better and further this time around. This is
a fun project for the typical "Home Depot Aquarist"! It takes only a
little advance planning and it does take some time and patience, but it is fun,
cheap and it works nicely. Yes, it is "cheap fun" too. You do have to
take some precautions since cement initially has a very high pH, but the
advantages are well worth while. You can make any shape you can imagine or mold.
Cement rock also grows coralline algae well. People have used various sands,
including aragonite sand and crushed coral, combined with Portland cement (a
greyish powder) and water.
Thanks goes out to Jake
Levi of Reef Life, Dick Perrin of Tropicorium, Bob Stark of ESV, Rick Greenfield
of CaribSea, Karen Holt "The Rocker" who is a creative cement reef
rock designer, and GARF. They have all helped with information, experimenting
and revitalizing the nearly lost art of making cement reef rocks. They have
pointed out some good information and advice on making cement live rocks for
live rock culture. Special thanks to Dallas Warren, Ph.D. student in Chemical
Engineering at the University of Melbourne, Australia. Dallas is also the
caretaker for OZ REEF Marine Park in Melbourne. Special thanks to James Wiseman,
a civil engineering graduate student at UC Berkeley. He works for Ben C. Gerwick
Inc. which specializes in hi-tech marine concrete structures, including coral
reef structure repair work using cement. See my web site to link to an
article on Gerwick News about this! Wiseman is also an avid reef aquarist. After
a lot of studying, experimenting and consulting, I am now able to compile what I
believe to be the most comprehensive cookbook for making, curing and growing
real good sure-fire reef-safe cement live rock.
According to professor P.K. Mehta's and P.
Monteiro's book "Concrete", a typical cement contains these compounds
(and their engineering names): calcium oxide, silicon dioxide, aluminum oxide,
iron oxide, magnesium oxide, sulfate, water, 3*calcium silicate (three calcium
atoms and one silicate) -- Called C3S 2*calcium silicate -- Called C2S. There
are other compounds that are combos of the above. For example C3A, C2A...
In general practice, there are 5 types of cement:
Type I: For general use, contains all of the five primary compounds. Type II:
Better Sulfite resistance and lower heat of hydration. Less C3A and C3S. Type
III: Maximum 15% C3A -- (Note: Cures faster, hence higher early strength). Type
IV: Low heat of hydration -- Mostly C2S. Type V: Best of the five types for
resistance to "Sulfate Attack" (That is corrosion of the re-bar inside
of a concrete section) This means that the cement itself is less permeable.
Conclusions as they relate to making cement rocks
for reef aquariums: You can use any type of cement powder that is available.
Type II or III might be slightly preferable in some ways, but don't worry too
much about this unless these are readily available. Use a high enough
water/cement ratio to ensure that ALL the Calcium Silicate is hydrated (bound
with water). Always use fresh water (not saltwater) to mix concrete. Concrete
gains most of its strength in the first seven days of curing. Type III cures
much faster and gains high strength early, hence this cement type is also called
"high/early" cement. Cure your cement rocks the first two days under a
wet burlap sack or with a plastic covering over it, or in an enclosure to
prevent fast evaporation and drying. It will gain higher strength if kept moist
during this setting-up time.
After this step you can put it in fresh tap water
to finish curing and leaching out high pH compounds and silicates. None of the
major compounds in HYDRATED (fully cured) cement look particularly harmful to
the aquarium according to Wiseman. The cement itself doesn't really corrode or
leach away into your aquarium after reasonable curing in water. In fact, some
aquarists have cured the two day old rock right in their reef tanks, but ONLY
while using CO2 dosing equipment. DO NOT do this unless you have a CO2 dosing
system to keep the pH from climbing when curing it in your aquarium. Otherwise
you can loose animals from high pH shock if CO2 dosing or proper curing is not
used first. Even then, you can still get more silicate leaching into your
aquarium than you might care for. This could also lead to aragonite sand
clumping as well. When cement/concrete is "curing" it is actually
absorbing water molecules - hydrating. After about 28 days it is mostly finished
hydrating or curing, but cement actually keeps hydrating VERY slowly
indefinitely. As it hydrates it releases calcium oxide and calcium hydroxide
which are two forms of kalkwasser. This is the main reason you want to cure your
cement in water for at least a month or two so these forms of kalkwasser can
leach out and not end up overdosing your aquarium and killing your reef life
with high pH. This has happened to some people who get too anxious, or are
uninformed.
Cement Reef Rock Recipes.
Try this good simple basic recipe to make some of
the cheapest porous cement reef rock around. It costs only about 9 cents a lb
using this recipe! Using a five gallon bucket, add 5 cups of common easy to find
type I/II Portland cement from Home Depot, a hardware store or building supply
store. Add 25 cups of crushed oyster shell from a farm feed store. Add six cups
of water and mix very thoroughly with a small hand held flower gardening digger.
Use rubber gloves to protect your hands from chemical burning due to extended
exposure to the high pH of the fresh cement - this is like soaking your hands in
supersaturated kalkwasser. Tip the bucket on a 45 degree angle and rotate or
roll it to help tumble and mix the cement well. Use the gardening hand digger to
mix the cement as you tumble it in the bucket. If the mix is too dry add a
little more water (slowly). Karen Holt tries for a final mix with the
consistency of cottage cheese. Others go a bit wetter than this, but not too
slushy. Many sand substitutes can also be used to make your cement if desired.
More on this later. You can get crushed oyster shell at the farm feed store
since it is used as a very common chicken feed supplement. And that, my friend,
is why THIS cement reef rock recipe is so "cheep, cheep, cheep"!
Do not make the final product too runny or you will
not be able to shape it into nice looking irregular shapes as well. An almost
slushy mixture that will still stand up just a little and take some shape (just
a bit) is just right for molding. In fact, James Wiseman advises that a wetter
mix not only assures that the silicates in the cement mix get hydrated and
bound, but a slightly wetter mix will produce more micro-pores or capillaries
throughout the cement for better bacterial colonization inside the rocks. On the
other hand, this can also weaken the cement just a bit, but usually not
critically so. On the other hand, don't make it too dry or the cement will have
too many large airspace gaps between sand or crushed oyster shell bits and it
will then be weaker than the mix that is too wet. Maximum hardness is mostly
reached after about a month of curing. Now, using rubber gloves, scoop handfuls
of it into a bed of dampened sand (or substitute) for molding and shaping your
cement into reef rocks.
Beforehand, you need to prepare this waterproof box
or container with sand, crushed coral, aragonite sand or crushed oyster shell.
Large plastic garbage can lids work well too. Dig irregular and creative shaped
molds in the slightly dampened sand. Karen Holt prefers using the crushed oyster
shell cement with about a 1:4 ratio of cement to crushed oyster shell, and uses
damp crushed oyster shell for the sand molding bed also. She makes some
interesting and intricate shapes with the cement that she calls "lace
Rock".
Another alternative box for the sand molding bed
that I have used is a large shallow Rubbermaid or Sterilite semi-clear plastic
"under bed" storage container with a lid. The lid can be used to cover
the container to keep the cement rocks from drying out while they set up for two
days. I found some of these cheap containers for only $4.50 at Wal-Mart. They
are made by Sterilite and are 2' long by 1.5' wide and about six inches deep.
Just right for making four larger rocks or eight smaller ones at once.
You can dig irregular holes in the damp sand
molding bed to form "molds" for making creative and or artistic
concrete rocks. I like to make holes through some rocks and mound up little
heaps of cement on them in irregular shapes so that they look more natural. This
is a great way to make arches, rocks with caves and long flattish rocks for
creating dramatic overhangs and more caves in your reef aquarium. I like to make
small cement rocks to place the large flatter rocks on in my reef aquariums.
This keeps more of the sand substrate surface exposed in my reef aquariums. You
can easily get up to 90% sand exposure this way. In HANDY Reefs with plenums and
sand, I sink these hand made cement support or pedestal rocks down to the top
screen just over an inch below the top of the sand. In Berlin style reefs with
an inch or two of sand, sink these base support rocks or pedestal rocks down
into the sand to the bottom of the tank for more solid support of the rocks
above.
Karen Holt made a beautiful hollow lacy thin cave
rock for my wife by burrowing out a deep hole in the sand molding box (she used
crushed oyster shell in place of sand). She fills the hole with a layer of
cement by dropping or dribbling small clumpy amounts of the cement mixture onto
the hollowed out molding bed so that the fresh cement clumps interconnect for
the most part, but it isn't just one solid layer. It ends up looking just a
little holey and porous. She then fills in over that with barely damp crushed
oyster shell to help it keep its shape as the cement sets up. When it sets up
for about two days you can use a stick to brush the sand (or oyster shell) out
and off of the new rock. The branching rocks that she makes are quite striking
also. The shape variations can be numerous and fun to experiment with.
**
I have used Karen's technique of dribbling cement
in layers and also putting sand or crushed oyster shell placed between parts of
layers to make rocks with interconnecting caves and tunnels running through
them. To do this, dig an irregular bumpy hole in the sand and dribble the first
layer, leaving some holes in it. Then fill the holes you left with barely damp
crushed oyster shell or sand and also cover up a couple other spots on the
cement with thick portions of the damp sand to help create hollows inside the
rock you are making. When you put more cement over this heap of sand, you build
it upward in layers of cement and separating pockets of sand. Just dribble your
next layer of cement mix over that and keep making holes and tunnels with the
intermittently placed pockets of damp sand. When it is has set up for two days,
use a wire coat hanger or a stick to dig and clean the sand out of the holes and
tunnels it has formed in the cement rocks. This can make really fun tunnelled
cement reefs rock! Get creative and have fun.
*****
IMPORTANT READ THIS!!! *****
You need to cure your cement rock WELL before
adding it to your aquarium, or it can easily boost the pH of the aquarium water
well up over 9! Since proper curing is the most critical part of cement reef
rock making, we'll go over the warnings here first, and then right afterwards
we'll cover some curing methods. Improperly cured cement rock which raises your
reef aquarium's pH, is not conducive to growing algae, fish, invertebrates or
anything! Improperly cured cement rock = death to aquarium. Others and I have
lost fish, live rock, live sand, live coral and more by getting too anxious to
introduce cement rock into aquariums. 12 hours or even a few days with a vinegar
curing process and then a week or two of fresh water curing didn't work with
larger rocks. It lowered the pH but not enough and it can weaken the more
delicate cement rock shapes somewhat and still not completely cure them or fully
lower the pH. When properly curing in fresh water is complete (five weeks or
MORE!) it should no longer raise the pH of fresh tap water and is now safe to
add to an aquarium in any amount. Before adding your new cement rock to your
aquarium, TEST the rock for high pH.
After you think your new cement rocks have cured
enough in water, change the curing water again and then let them set with a new
change of fresh water covering them for about four days. Do not aerate the water
or even keep it moving during this final curing time before testing the pH.
After four days of this final soaking in stagnant water, stir the water the
cement is in just before you test the pH of the water. If the pH has risen to 8
or higher then continue curing another three days (to complete another week of
soaking) before changing the water again, letting it set four more days in the
new water, and then testing the pH of the water again. You can aerate the water
during curing, but not before testing the pH or you will get a false low pH
reading due to the aeration precipitating out the calcium hydroxide and calcium
oxide that causes the high pH.
The object is to find out if the cement is still
leaching, not to see if you can cover up the signs of this final curing and
leaching. More on complete leaching and pH rebound at the end of this article.
Once the cement is fully cured, I no longer detect these pH raising compounds or
silicate leaching. DON'T use cement rock until you KNOW that it will not raise
the pH of your tank to the point of killing things in it. This high pH will also
cause binding and severe clumping of an aquarium's aragonite sand substrate. So,
no matter how you choose to cure your cement rock, TEST IT for pH before using
it in your aquarium. It makes absolutely wonderful reef aquarium rock if it is
properly cured first. Save a reef, cure your rock!
*********************************************************
Jake Levi and I spent a few months in the summer of
1997 doing some long distance joint research on curing and lowering the pH of
cement reef rocks. This was after we had both lost reef life due to improperly
cured cement rocks when following directions that advised 12 hours or more of
initial vinegar curing and then a week or two in fresh water to finish curing.
Apparently our cement rocks were NOT cured with this short-cut method. We wanted
to know how long it really takes to lower the pH of cement reef rocks to make
them totally reef-safe. We had experienced no problems in our aquariums when
using several small flat cement "cookies" for attaching coral cuttings
to, that had been cured in vinegar and then water. We later found that the small
amount of rock (usually less than two cups of uncured small cement
"cookies" per 50 gallons) is not enough to raise the pH of the vastly
larger aquarium volume very much. We have attached many new coral cuttings to
these small cookie sized cement rocks.
Initially, when we started comparing notes, we
found that we both had the same pH problem with the medium to large cement reef
rocks we had been making and couldn't quite figure out why they would not cure
quicker as the directions had said they would. We had both had losses from the
high pH of cement rocks that we both assumed were cured. We had tried vinegar in
different strengths and varying lengths of time, and then into fresh water for a
week, or even two, after the vinegar bath. But, no matter which combination we
used, no amount of vinegar or water afterwards, seemed to do the trick for these
bigger rocks in just one or two weeks. We tried variations on using vinegar or
hydrochloric acid to treat the rock with initially, and then soaking it in fresh
water.
We found that it takes at least five to six weeks,
in just fresh water only, to cure the cement and lower the pH. The average
hobbyist has access to buckets, garbage cans and such. That is what we recommend
using for curing containers. After all was said and done, we concluded that you
can skip the vinegar or acid pre-treatments and just go for the fresh water
treatment only. The calcium oxide and calcium hydroxide (forms of kalkwasser)
that slowly leach out of the cement rocks, still take time to leach out of the
bigger rocks whether you use acid to neutralize it after it leaches out of the
rocks or not.
We used buckets and big plastic garbage cans for
the bulk of our curing experiments. I covered my cement reef rocks with fresh
water and changed the water once or twice a day for a month by putting a garden
hose in the bottom of the rock curing garbage cans and trickling it at a rate of
one or two water changes per day. If you don't change the water at all, the
process of lowering the pH slows down. However, Jake was still successful with
changing the water just once a week for 4-5 weeks. He prefers six weeks to be on
the safe side, and then still tests for proper pH and gives the rocks a final
two or three weeks in saltwater to be really safe before adding large quantities
to a reef aquarium. I have even added a power head to a large plastic garbage
can full of rock to circulate the water, but this is not absolutely necessary.
Dick Perrin uses about a half cup of muriatic or hydrochloric acid in a
55-gallon plastic barrel full of water and half full of cement rocks with an
airlift tube made from PVC pipe to aerate and circulate the water as curing
takes place. This method still takes time to get the full curing. It does lower
the dramatically high initial pH of the curing water and takes the very worst
edge off of the pH. This does not provide complete curing or leaching though. I
do NOT recommend using acids like this due to the dangers involved, including
chlorine fumes!
Keep the curing rocks out of reach of pets and
children since the curing water initially has a high pH much like liquid drain
cleaner mixed with water does. You can test the pH each week and watch as it
stays level, and then starts slowly dropping from above 9 down closer to the pH
of your tap water by the end of a month, or usually longer. It can take up to
two months sometimes to get a truly total cure with a pH in the 7 range. Both
Jake and I noticed another thing that happened when the pH finally dropped and
curing was near complete. When curing outdoors, even in strong indirect
lighting, we noticed brown algae starting to grow on the cement as it becomes
cured. This brown algae-like growth, that can also be long and stringy, is
actually filamentatious diatom growth. This is a good sign that the pH has
dropped enough so that life can now live on these rocks. You will notice another
thing if curing in stagnant water without circulation. The top of the water
develops a crust of calcium carbonate as the calcium oxide and calcium hydroxide
combine with CO2 at the water's surface. This crust gets thinner with each
subsequent water change. In summing up our curing tests from last summer, Jake
Levi's method of curing cement reef rocks using only weekly water changes seems
to be more practical and the least hassle. I like this simpler method better,
even if it takes just a bit longer.
Jake also has a unique recipe for cement rock which
he affectionately calls "Rock-a- Roni". Yes, he actually uses pasta in
the mix! He adds full pieces of dry ziti to the cement mix and molds the rocks
with the many pieces in them. This creates long tunnels through the rocks for
better colonization of bacteria and micro fauna. He keeps the proportion of ziti
down to 1/5 of the cement volume. More ziti makes the mix crumbly. He cures the
Rock-a-Roni extra long to dissolve the pasta out of the cement. He uses a hose
with sprayer to wash out the soft ziti after about a month of soaking. It makes
a very nice porous cement reef rock. Another variation or special touch he
sometimes adds to some of his cement reef rocks is pasta shells. He presses
various sized pasta shells into the surface of freshly formed wet cement rocks.
They come off easily after the cement sets up and leave interesting and unique
shell impressions.
Go make a batch and have fun! There are other
variations that some people use. We'll look at them now. Don't be afraid to try
some variations and get creative. Just be sure to cure it well, then test the pH
before using it in your aquarium. Here are some other sands or rock products
that some people use in their cement for live rock. We already mentioned crushed
oyster shell which makes a more porous and much cheaper rock than some other
options. You can also use crushed coral of any brand or even crushed dolomite
from your fish store, used for aquarium substrate, or dolomite from your garden
center used as a soil additive. Oolitic aragonite sand from CaribSea or ESV
Company also works well. Bob Stark of ESV has had great success with oolitic
aragonite cement and also crushed oyster shell cement for several years.
Some people are nervous about using crushed oyster
shell which is cheap but higher in phosphate and silicate, which does not leach
perceptibly into your tank after proper curing. It has not in mine. Others are
still worried about some sources of dolomite, but it has been used successfully.
Even white #20 pure quartz silica sand from the hardware store has been used,
not only for making cement but for reef aquarium sand substrates too. While this
silica sand may look fine and work fine as a substrate, it adds no calcium and
does not buffer your aquarium water like aragonite sand substrates do. It does
not seem to leach any perceivable silicate into your aquarium either. I do NOT
recommend using ordinary sand or gravel used for common cement mixes or
pre-mixed dry bagged "post mix". Ordinary gravel and rocks may have
higher levels of metals in them, or other substances that you don't want in your
saltwater aquarium. The point here is to use sand, rock or gravel that is
reef-safe.
Variations for Making Cement Reef Rocks.
Some people have a real problem finding type II or
type III Portland cement that has often been recommended. If you really want to
use it, call around to the cement or masonry suppliers in your area. Karen Holt
has also used the much more expensive and harder to find pure white Riverside
cement with a lot of her rock making. Type III cement is used in cold weather
and for cement work exposed to saltwater. In my area I have a hard time getting
it until about the first frost in autumn. Type II may be the best of these two
cement types. But, regular type I or type I/II Portland cement will harden very
well after about a month and are just super and very usable for making cement
rocks. Type I/II Portland cement is the most common and can be found at almost
any lumber yard, hardware store or home improvement center. Many people have
used it very successfully. I now usually just use type I/II and have had good
success with it and I highly recommend it.
Type I/II Portland cement normally comes in 94 lb
bags for around $5 at Home Depot. I have even used Portland cement powder to
make the molds for forming my cement rocks. I still like wet crushed oyster
shell or even finer aragonite sand for making molds. Another option is to mix
finer aragonite sand with Aruba Shell aragonite from CaribSea for a very nice
effect. I usually just use the crushed oyster shell for the sand molding bed
now. It is the cheapest and works very well also. Others and I have varied the
preferred formula for mixing cement reef rocks and have still had very good
success.
Another neat variation on making rocks from cement
was sent to me by Paul Baldassano. He has always used Sackrete mortar mix to
bond rocks together. He sent a picture of a recent conglomeration rock that he
made using many pieces of old coral skeletons and rocks cemented together into a
very nice looking irregular arch about a foot and a half long. He used about 3
cups of ready mix Sackrete mortar mix to bond the rocks and coral skeletons
together into one final rock sculpture. The sculpture is then allowed to set up
for two days, and then it is put in fresh water to cure like regular cement
rocks.
What do
you do with those spare small pieces of coral rock?
***
Use cement
mortar mix to conglomerate them into one big rock sculture for your aquarium.
Paul Baldassano has been doing this since the 1970's!
***
Here are two more variations for making cement
rocks. I sometimes use a cement to crushed oyster shell ratio of 1:4 or even 1:3
rather than my general recipe above using 1:5. This makes thick or less porous
cement mixes for making stronger delicate rock structures with lots of
interconnecting caves and tunnels. This extra cement fills in some of the air
gaps between the crushed oyster shell bits. When using the general 1:5 recipe
above, the rocks are just a bit weaker, but they are so porous that you can run
water right through them! This is great for growing tiny rock dwelling critters
and good bacteria.
Another way to make very strong cement rocks may or
may not be practical for some of you, but here it is for the fearless, anyway.
James Wiseman pointed out that Gerwick Company also uses a special additive
called silica fume with their cement mix that they use for reef repair in the
ocean. It does two things. It can make a cement that hardens to a strength
rating of over 10,000 PSI! It also lowers the pH of the cement somewhat. I still
recommend curing it just as long for reef aquarium use since it still leaches a
lower amount for just as long as regular cement. Silica fume is a very light
grey-white powder and is nowadays used to strengthen the cement used for high
strength structures that must hold up extra well and extra long and/or be more
freeze damage resistant. I only use silica fume when making the delicate
structured rocks with lots of tunneling in them. Otherwise I want an overall
more porous rock with the regular recipe of 1:5 or maybe even 1:4 cement to
oyster shell ratio.
Silica fume can not be found at Home Depot or
hardware stores. You can get silica fume from cement additive supply houses or
from some cement ready-mix plants. If you really want to try some, then call
around to find it. It is rather expensive at $15 to $25 for a 25 lb bag! It is
NOT a must-use item. One bag will be much more than the average aquarist will
ever use. If however, you are going to make a whole lot of cement rocks, then
this will raise your total cost of cement rocks from about 9 cents per lb to
about 11 or 12 cents per lb. There are five - 5 lb bags of the silica fume
powder in each 25 lb bag. It goes a long way since you only use 5% replacement
by weight of the Portland cement. You only use one 5 lb bag per each 94 lb bag
of Portland cement! It is twice as light weight as Portland cement so you end up
replacing about 8- 9% (by volume) of the Portland cement with the silica fume.
James Wiseman cautions that you should not use more than about this 5% amount by
weight or you may get additional silicate leaching even after the cement has
cured. I use 4 and 1/2 cups of Type I/II Portland cement with 1/2 cup of silica
fume powder. This 10% silica fume by volume which is 5% by weight. I mix this
with 20 to 25 cups of crushed oyster shell and then I add water and mix it well
until it is the consistency of cottage cheese - about five to seven cups.
Depending on the desired porosity of the final cement that I want, I use more or
less oyster shell. More crushed oyster shell leaves more small air gaps between
oyster shell chips. This porousity technique seems to work best with oyster
shell. I can slowly run tapwater right through a finished porous rock like this.
But, using way too much oyster shell will weeken the cemnet with too many air
spaces.
Results of latest cement curing tests:
In the last couple of months I've been doing
additional multitudes of tests and experiments on making cement reef rocks and
especially on how best to cure them. I've also been digging up even more info
sources in these areas too. I've found that it is best to cure your cement rocks
in fresh and not saltwater - initially at least. Curing in saltwater from the
beginning can weaken the cement to some degree. You can finish off your curing
with saltwater though, and not experience any noticeable weakening. Acid or
vinegar curing also weakens - probably much worse than saltwater curing can.
Don't use acid or vinegar curing. Save your vinegar for salads. I like apple
cider vinegar best since it adds that special tang to my homemade salad
dressings! If you want to speed up curing a little bit, it is much better to do
so by strongly bubbling or aerating the curing water. This should be as good as
using more water changes to speed up the process a little, as I'll explain here
shortly. Very cold icy curing water during outdoor winter curing really slows
down the process too.
Too much silica fume weakens the rocks a lot. Don't
use over 5% (by weight) or you might end up with too much silicate leaching
which you will get anyway until the rocks are cured. I tested 5%, 10% and 20%
silica fume cement mixes in hopes that the higher percentages would be lower in
pH and maybe not even need curing! Not so! The 20% ones were noticeably fragile
and breakable. The pH of the stagnant fresh curing water was only very slightly
lower when curing cement rocks made with the 10% or 20% silica fume mixes rather
than with the 5% mix. I later found that you actually CAN load a tank with brand
new 5% silica fume rocks and keep the pH from going too high simply by providing
excellent aeration, but I wouldn't anyway. You will still get a lot of silicate
leaching with this in-tank curing (with or without silica fume) as it cures. It
still has a high pH creating potential (9'ish as opposed to 11'ish) and still
must cure even though the pH is lower. Also, if you don't provide high enough
levels of aeration, the pH will still go up and hurt things in your aquarium -
don't try this in your tank for both of these reasons!
I'm sticking with the out-of-tank fresh water
curing whether using low volumes of cement rock or whether using silica fume or
not. Curing and subsequent pH leaching is still variable depending on the
Portland cement you use and the water amount you mix it with and your tap water
and so on. Small thin rocks cure more quickly or at least the pH drops to
acceptable levels more quickly, but a full curing still takes time. I can cure a
small rock or two right in my aquarium in about two weeks, but you still don't
want to do this.
I also noticed what I call a saltwater "pH
rebound" when I put cement rocks in saltwater that were cured in fresh
water first. This pH rebound is mild, so you may never even notice it. If you
cure your cement rocks in fresh water as instructed until the pH is fully
lowered, and then transfer them (like normal) to a reef tank you probably won't
notice any of this pH rebound since aeration in the reef tank masks this mild pH
rebound. Why does aeration hide this pH rebound? CO2 introduced to your aquarium
from aeration in modest amounts combines with the released calcium oxide and
calcium hydroxide (the two forms of kalkwasser) to make calcium carbonate which
can buffer your aquarium slightly. It raises the KH, which you can watch happen
in your aquarium with a test kit! On the other hand, if you want to see this pH
rebound in action then put the fresh water cured cement rocks in a bucket of
stagnant saltwater. You will then be able to monitor the pH as it slowly climbs
to about 8.6 or higher within a few days. If you then simply add an open ended
air line to aerate this same curing bucket with saltwater and freshwater cured
cement rocks, the pH drops rather quickly again while the KH goes up just a
little as a result of introducing enough CO2 from the air to create calcium
carbonate from the calcium hydroxide and calcium oxide released by the cement.
Even with this slight pH leaching rebound when you transfer the freshwater cured
cement rocks into you reef aquarium, I have not seen noticeable silicate
leaching at this point. You just want to make sure that your aquarium has
adequate aeration when you add any cement rock, even when it seems fully cured.
It would be a good extra precaution to make sure your tank is very well aerated
when you add the cured rocks to it. Use good water surface movement and use your
protein skimmer. You could also use a supplemental air stone in the tank.
While still curing the cement rocks in freshwater
you can also drop the pH of the curing water with strong bubbling/aeration, but
amazingly the KH also tends to go down with the drop in pH in fresh water. After
intensely aerating a bucket of curing cement rocks in fresh water for a few
days, it is uncommon for the KH to remain above 3 or 4 dKH. This appears to be
because the calcium carbonate seems to precipitate out of solution faster in
fresh water. It precipitates as a whitish powdery dust on the bottom of the
container. This has happened much more readily when curing in freshwater. If you
just let the curing water sit stagnant as I often do, then just a few days after
you start curing your new cement rocks in stagnant freshwater, the pH may climb
to as high as 11 or 12. A reading of 20 dKH is also common while curing in
stagnant fresh water. The pH drops on a curve with subsequent water changes,
with the most leaching occurring earlier and the last of the curing being slower
and seems to drag on a bit.
Well, it looks like it's time again to say, "Soooo
long!" There you have it, the best options and some alternatives for making
live rock from cement and other rocks. You can now make and shape some of your
very own rocks in the fun shapes and sizes you always wanted but could never
find. Perhaps that's the best part about making your own cement reef rocks. As
for the other rocks mentioned at first, they are very handy if you don't want to
get messy or wait for cement reef rocks to cure for a month or two. I've gotten
so good at mixing and molding cement rocks now, that I can practically do it in
my Sunday clothes, plus rubber gloves of course. But, some times you need some
base rock to set up a reef tank, and you need it right now! When you don't have
time to mix it, mold it and wait for it to cure, the boxes of CaribSea dry Reef
Rocks come in very handy! Using a combination of both types of rock has worked
very well for me. You can grow extra live rock to trade for corals, fish and
equipment also. Do check out my new web site at http://www.geocities.com/CapeCanaveral/Hangar/6279
if you haven't been there already. Or, if you have seen it already, check it
periodically for new additions and changes which are now listed in a
"What's New..." section on the menu. You can contact me through the
web site or send e-mail directly to me at EZreef@yahoo.com.