A Simplified Water Top-Off System for Aquariums

by J. Charles Delbeek M.Sc.

With the advent of open aquariums, especially reef type aquaria, water loss due to evaporation has become a real problem. When salinity is critical, the regular addition of top-off water becomes vital. This can become rather time consuming, and one can quickly become a slave to one's tank. Although there are some commercial solutions to this problem, many are rather costly. I have implemented a system that is inexpensive, low cost, low maintenance, requires no power, easy to use and very precise. My thanks to Norm Chong of the Marine Aquarium Society of Toronto for introducing me to this technique.

The illustrations show a device that is commonly sold in hardware stores as part of a float valve for humidifiers. There are a number of models available, most of which should be suitable. The most important consideration is the materials used in their construction and necessary for their operation. The model I chose to use, utilized a brass cotter pin as a pivot point. I replaced this with a plastic toothpick. The unit illustrated consists of one moving part which is pivoted such that when upward pressure is exerted on the float, a plastic pad is forced against the nipple opening of the water inlet. When the water level falls, the opening is uncovered and water from a reservoir, located above the float valve, flows through and into the sump by gravity. Since the sump I originally used this device in had an operating volume in the last chamber of about 2 gallons, the slightest loss of water resulted in a noticeable drop in water level.

This resulted in the float switch being able to maintain a constant salinity in the tank rather easily. The float angle can be adjusted with a set screw in this particular model, so it was easy to fine tune the desired water level in the sump.

In addition to the humidifier float valve, I used 1/4 inch clear Tygon tubing, a 1/4" nylon valve and a five gallon reservoir. All of these components were purchased at a wine making shop, which is a great place to find food grade tubing, fittings and containers. Eventually I used this setup to dispense kalkwasser as make-up water to the tank. As a result the device had to be cleaned about twice a year to remove calcium carbonate build-up along the water path; the nipple opening never clogged though. This device can also be used to add trace elements, buffer solutions, saltwater, whatever, in slow, easily controlled amounts.

There are a few problems that I encountered when using this device that you should be aware of. For example, if you are using a protein skimmer that is set to produce a wet foam, you will loose saltwater from the system. This device will replace that lost saltwater with freshwater. As a result, the water will gradually drop in salinity. You must therefore regularly check the salinity of your water and adjust it accordingly. Likewise, if you fiddle with your pumps and valves, resulting in the sump level rising and falling, this device will add some freshwater.

Finally, when choosing the size of your reservoir, take into account your tank size. If something should go wrong with the float valve, the entire contents of your reservoir could be added to the sump. How much freshwater/kalkwasser could you aquarium absorb without a large drop in salinity or a large increase in pH? For this reason I do not recommend reservoirs larger than 5 gallons for large systems (100 gallons+).

This article first appeared in the October, 1989 issue of Freshwater and Marine Aquarium magazine.

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