I bought several float switches from the source which you can find by doing a net search for floatswitchs.net ....
I bought four of them, and am completely satisfied. They are only 6 bucks a piece.. I built a small housing out of PVC to house the switch. The switch is reversable so that floating up will either turn on or off the air pump, so I set one for level control, and one to shut off the air pump if the level should rise too high... Then wired in the two float switches to an extension cord that goes to the airpump. The high float switch is always on unless the level gets too high, and the low float switch is always off , until the level drops below my desired tank level.
This has worked flawlessly now for several months, and my tank level does not fluctuate more than 1/16th of an inch.
I have two spare switches just in case, but so far have not needed to use them..
I have never sat and timed it exactly, but I would say that the air pump turns on and off between two and three times an hour during the day when my lights are on and evaporation is at its peak, and maybe once every two hours during the night...
I have a Refugium that sits on a ledge next to and above my tank that the top off water feeds to. My refugium is fed by a pump in the main tank at 250 GPH, and gravity flows back to my main tank. The 5 gallon tank that holds the top off water sits next to the Refugium and the air pump only has to pump the water up about 14" to feed into the Refugium. The air pump I use also has a varible control and two outlets, which are both hooked up to the line that pressurizes the container that holds the top off water.. by adjusting the air pump, I can control the flow from the top off water container to the Refugium also. I have found however that it works find on the highest setting, but when I set it up, I thought that might be too much flow.. it is not, the air pump never stays on more than 30 seconds..
I also happen to have an Eheim Wet Dry model 2229 which actually raises and lowers the level of my main tank as it fills and empties back into the main tank, so the air pump always goes on and off also based on the operation of the Eheim. When the Eheim fills, the main tank is at its lowest point, that is when the air pump comes on. As the Eheim starts pumping back into the main tank, the level rises and shuts off the air pump.
I am not sure how much different this setup would be in a main tank where the level stays static. I would imagine the airpump would stay on longer because it would not shut off until the level of the tank rises to close the float switch, but in my case, when the Eheim fills, the level of the main tank drops anyway, but when it needs top off water it drops lower and turns on the air pump. As the Eheim pumps water back to the main tank of course, the float switch rises and shuts off, much quicker than it would in a tank with a static level.
I was going to move the Eheim to my sump actually, but after thinking about how this works so well, I have decided to leave the Eheim in my main tank and hide the intake for the Eheim in a sort of in the tank overflow box to protect any livestock from getting sucked up into the Eheim intake. I almost lost my Anemone to that once.
So, while my setup is not going to be typical, I still think it will work quite well on any tank... and the whole thing only cost me less than $35 including the four float switches.. The only difference being that in a tank that has a static water level, the air pump will probably stay on quite a bit longer to raise the level of the tank enough to raise and close the float switch...
Hope this was not too confusing....
Dave
