Dosing Pumps Revisited

The LiterMeter by Spectrapure
Back in 1996 I wrote an article entitled “Methods for Replacing Evaporated Water and Dosing Limewater” (Aquarium Frontiers, Vol.3 No. 4). In it I described a variety of techniques and devices for replacing evaporated water and dosing trace elements, fertilizers and so on in marine and freshwater aquariums. One of the devices I discussed was a peristaltic pump called the Flexi-Flo-II. It was a hospital surplus pump that was manufactured by Ross Laboratories and sold through Lifereef Filter Systems. Based upon my experiences with this particular pump I concluded that these types of pumps are unreliable and unsuitable for use as aquarium dosing pumps.

Since then I’ve had the chance to try two new peristaltic pumps sold by Two Little Fishies (Vario Dosing Pump) and Spectrapure (The LiterMeter), and I’ve changed my opinion in a big way. Not only do I now feel that peristaltic pumps are a viable option for use in aquarium applications, but these new pumps probably represent the best options as dosing systems. Using the same criteria from the original review, both of these new pumps scored higher than the other systems previously examined.

For those of you unfamiliar with peristaltic pumps, let me briefly describe how they operate. I found the best description of their operation in the 1998 Cole-Parmer catalog. Peristaltic pumps are also called tubing pumps. They consist of two parts: a rotor and housing. The tubing is placed between the rotor and housing where it is occluded (squeezed) by rollers. After being pinched, the tubing behind and between the rollers recovers its shape. This creates a vacuum and draws fluid behind it. A “pocket” of fluid is created. The rollers on the rotor continue to move across the tubing, “pushing” this pocket of fluid. The speed of the rotor and the inside diameter of the tubing determine the flow rate. As both increase so does the flow rate.

The beauty of peristaltic pumps is that because the fluid is confined to the tubing, the pump cannot contaminate the fluid and the fluid cannot contaminate the pump. In other words, the pump itself cannot be damaged or affected in any way by the fluid in the tubing. The type of tubing can be matched to the type of fluid being pumped. For example, Two Little Fishies states that they have chosen a “special rubber part” (tubing) for their Vario Dosing Pump based upon its suitability for use with kalkwasser (a concentrated solution of calcium hydroxide).

Speaking of the tubing, the life of the tubing “pump” is determined by what you are dosing, its resistance to that chemical, the abrasiveness of the liquid/slurry, the speed of the rotor and the frequency of the pumping. For example, a slurry of kalkwasser would be much harder on the tubing than if you were dosing plain water. Charles Mitsis of Spectrapure told me that based upon some testing that he conducted, the tubing on the LiterMeter could theoretically last as long as five years. This may be so, but because this tubing is not an expensive item, replacing it at least yearly is a good maintenance practice.

The Vario Dosing Pump by Two Little Fishies
Some of the common features of the Vario Dosing pump and the LiterMeter include:

  • There are no traditional pump heads, impellers, seals or valves to clog, clean or replace on either pump. The only required maintenance is to periodically replace a small piece of tubing. In the cases of the Vario Dosing Pump and The LiterMeter, that’s a five-minute job.
  • They can both run dry for an indefinite period of time. At some point in time every aquarist will let their reservoir run low, resulting in their dosing pump running dry. It’s good to know that these pumps won’t burn out.
  • Up to a limit, they can both pump a slurry without fear of clogging. This can be an issue for aquarists who wish to dose a milky solution of kalkwasser.
  • Both pumps are self-priming. There is no need to keep the pump head flooded and the pumps can be located above the reservoir.
  • Related to the above, both pumps are non-siphoning. This means that they can be located below the reservoir without fear of siphoning and without the need for check valves. My advice is not locate the pump below the reservoir unless it is absolutely necessary. Although it’s unlikely that either pump would back-siphon, I prefer to be safe than sorry.
  • As I stated previously, the tubing is the pump chamber. Therefore, the fluid being pumped does not contact the pumping mechanism. Again, this is advantageous when that fluid is a corrosive or caustic one, such as kalkwasser, which has a pH of approximately 12.0. Also, it is unlikely that either pump will clog. This is probably their biggest advantage over other dosing systems.
  • The design of both of these pumps eliminates the need for check valves, which are used in diaphragm dosing pumps, such as the Reef-Filler. This is important because check valves invariably fail and need to be cleaned, especially if you are pumping a heavily viscous fluid, such as kalkwasser.
  • Both pumps install in a matter of minutes. There are only two connections (a line in and a line out) and, in the case of the Vario Dosing Pump, only two controls. One is an on/off button and the other is a rotary speed controller that governs the speed of the rotor mechanism
  • The rotor mechanism is the only moving part and it’s maintenance-free.
  • Both pumps are very energy efficient. The LiterMeter consumes less than 6 watts of electricity in its running mode.
  • Both pumps can use ╝-inch polyethylene tubing for the input and output lines. This tubing is stiff, yet flexible. It’s resistant to kinking, yet it can be easily directed around bends and turns. It also can be “hard-piped” through the use of mini-fittings, which are sold by Spectrapure. It’s always a good practice to hard-pipe the tubing so that it can’t accidentally fall out of your aquarium or sump. Believe me, if you don’t, one day it will. I hope your aquarium setup doesn’t sit on a rugged floor.
  • Both pumps are relatively quiet and can be used in a living room or bedroom setting.

    The Vario Dosing Pump

    The Vario Dosing Pump is a well-made peristaltic pump that’s imported from Germany by Two Little Fishies. It is approximately 5 inches square and weighs about 2 pounds. According to Two Little Fishies, this pump was specifically “engineered for dosing kalkwasser, trace elements or for topping off evaporated water.” The flow rate is adjustable from 18 milliliters per minute (ml/min) to 10.8 liters per hour (L/h) through a recessed screw on the face of the unit. It’s accurate to within ▒5 percent of the stated rate. Continuous operation is possible up to approximately 2.2 L/h. The tubing “pump” has an outside diameter of 6 millimeters and an inside diameter of 4 millimeters. It’s capable of pumping a milky solution of kalkwasser without a concern for clogging. The pump is self-priming. It has a maximum lift height and head pressure of 10 meters. The pump is supplied with two plastic brackets that allow it to be mounted to a wall or cabinet. Based upon the maximum stated flow rate, I estimate that this pump can service aquariums up to 1000 gallons in capacity. The retail price of the Vario Dosing Pump is approximately $269.

    I have been using the Vario pump on a large reef aquarium to replace evaporated water with kalkwasser. It’s worked very reliably for me and hasn’t required servicing of any kind in the almost three months that I’ve had it in service. Even though the Vario pump can be run continuously, I have it on a lamp timer that turns the pump on at dusk and off at dawn. The purpose of this is to limit the dosing of kalkwasser to the nighttime hours only. The pH of the aquarium becomes naturally depressed after the lights go off due to the production of CO2 by the algae in the aquarium (both free-living and symbiotic). Dosing at night allows you to dose more kalkwasser with less concern for the pH becoming too high. Dosing in this manner also tends to maintain the pH level at a relatively steady state through the entire day.

    Setting up the Vario pump was quick and easy. I anchored one end of a piece of ╝-inch flexible polyethylene tubing into a 44-gallon container of kalkwasser and the other end was connected to the input side of the pump. It’s simply pushed into the tubing and secured with a plastic cable tie. Another length of the same polyethylene tubing was connected to the outlet of the pump and extended into a small compression fitting at the top of my sump. The pump plugs directly into any 120-volt electrical outlet and is activated by an on/off switch at the top. The switch is encased in a rubber shield to make it water-resistant. That’s a very nice touch.

    The LiterMeter

    The LiterMeter is plumbed similarly to the Vario pump, but it is a little more complex to set up, has a few more “features,” and it operates a little differently. The LiterMeter can dispense from 50 milliliters to 99 liters over a 24-hour period. At its maximum output the LiterMeter is operating at a 33-percent duty cycle. It can be considered suitable for systems in excess of 1000 gallons. It too is kalkwasser-safe and self-priming. The supply tank can be located as much as 10 feet below the LiterMeter and it can pump to a height of 16 feet when the supply tank is at the same level as the pump.

    The LiterMeter is rectangular in shape. It measures approximately 4 inches by 7 inches and weighs just one pound.

    The biggest difference between the LiterMeter and the Vario pump is that the LiterMeter can be pre-set to dispense an exact amount of fluid over a 24-hour period. After the LiterMiter has been plumbed and is in its permanent position, it has to be calibrated. This is simply done by timing how long it takes the pump, when running continuously, to fill a 500-ml cup. The resulting flow rate, in ml/min, is dialed onto the “Calibration” panel on the front of the unit.

    The next step is to determine exactly how much fluid you want the LiterMeter to dispense over each 24-hour period. This amount, in liters per day (L/day), is dialed onto the “Daily Total” panel, which is also on the face of the unit. A microprocessor controls the pump and runs it just long enough, in 150 separate increments throughout the day, to deliver this total amount. For example, if the daily total were set to 3.75 liters, the pump would dispense 25 ml of fluid 150 times over the course of each 24-hour period. The 150 increments are evenly spaced over this 24-hour period by the built-in microprocessor.

    It would be wise to re-check the calibration periodically, especially if you are dosing trace elements or an iron supplement that requires precise dosing. The LiterMeter is very precise, but the output can change over time as the tubing builds up with material, particles or slime. The tubing will also stretch as it ages, and this will affect the output as well. The Vario pump can also be roughly calibrated to dispense a set amount of fluid each day, but this calibration must be completely recomputed whenever the total daily amount is changed.

    The other difference between the pumps is that the LiterMeter offers an optional float switch. The float switch can be placed at a particular level in your tank or sump. It will prevent the Liter Meter from operating when the water level reaches this pre-determined position. This offers insurance against over-dosing and eliminates the need to reset the pump as the evaporation rate in the aquarium changes throughout the course of the year.

    So which one should you buy? Both pumps are well-made and reliable, and you wouldn’t be making a mistake by buying either one. They both come from reputable companies in the aquarium industry that offer excellent customer support.

    Some of the possible advantages of the LiterMeter include:

  • The LiterMeter can be precisely set to dose a specific amount of fluid each day and this setting can be changed relatively easily while still maintaining that precision.
  • The LiterMeter offers an optional float switch.
  • Both the ╝inch polyethylene feed and supply tubing are supplied with the LiterMeter.
  • The head of the LiterMeter can be rotated at 90-degree intervals. This offers some additional flexibility in terms of mounting positions and mounting options.
  • Both pumps are relatively quiet and non-obtrusive, even in a bedroom setting, but the LiterMeter is less noisy than the Vario dosing pump.

    Some of the considerations in favor of the Vario dosing pump include:

  • It comes with a bracket that allows it to be mounted firmly to any surface that accepts screws. The LiterMeter is supplied with Velcro tape for mounting purposes.
  • The Vario pump is less complex to set up. In fact, I lost the one-page instructions that came with the pump and I was still able to set it up with no problem.
  • The rotor speed is adjustable by a recessed screw that is covered by a cap. This is important if the pump is situated in a public area or within the reach of curious children. The adjustment controls on the LiterMeter are easily changed through two toggle switches and rotary dials on the face of the unit. Depending upon your perspective, this may or may not be advantageous.
  • The on/off switch is protected against water intrusion by a rubber cover. This is a good precaution for an electrical device that’s intended for use in a wet area.

    Still confused? If you are looking for a pump to dose trace elements, iron supplements or one of the two-part balanced calcium/alkalinity supplements, then the precision dosing offered by the LiterMeter is an important consideration in its favor. If you simply want a pump to replace evaporated water, then the Vario pump is an uncomplicated and reliable choice. It’s your call.

    For more information or to order a LiterMeter, you can contact Spectrapure by phone at (800) 685-2783 or it can be obtained online through Monolith Marine Monsters. Two Little Fishies has an informative web site that offers more technical information about the Vario pump at Two Little Fishies.

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