|The LiterMeter by Spectrapure|
Since then Ive had the chance to try two new peristaltic pumps sold by Two Little Fishies (Vario Dosing Pump) and Spectrapure (The LiterMeter), and Ive 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|
I have been using the Vario pump on a large reef aquarium to replace evaporated water with kalkwasser. Its worked very reliably for me and hasnt required servicing of any kind in the almost three months that Ive 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. Its 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. Thats a very nice touch.
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 wouldnt 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:
Some of the considerations in favor of the Vario dosing pump include:
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. Its 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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