Backyard Aquaponics
A place to discuss aquaponics

Float switches can fail, not likely but they could.

I'm wary of float switches since they can get easily fouled depending on what type they are.

So many people with simple systems where they are pumping from the fish tank, will elevate the pump a little bit to ensure if a HSM happens from some plumbing coming unhooked that they can't pump their fish tank completely dry. (most common thing would be the pipe to the grow beds getting knocked down so it is pumping the water out of the system.) Anyway, should this disaster happen, if the pump is elevated, perhaps the fish will survive the disaster long enough for you to see it and re-fill the tank. Depending on the pump, it may or may not survive being run dry but if the pump was at the bottom of the tank you would wind up with not only the dead pump but probably dead fish too.

As to the solids. Perhaps having the pump at the bottom would help a little bit on moving solids along through the system but I find that any system with good water flow/circulation and a few fair size fish, the solids stay stirred up enough to get sucked up by the pump and go to the grow beds even with the pump elevated off the bottom of the tank a bit.

I have a stock tank valve setting about 2' above bottom connected to my water well. It works as a safety zone and handles water make ups. Thanks Jerry

The auto top up valves do help and I highly recommend them but if there is a major disaster of the pump actually pumping water out of the system due to a busted pipe or something not glued being knocked out of the grow bed, the top up valve will probably not keep up with the pump.

A magnetic reed float switch is what I use. The magnet is sealed in an inner chamber so there is no fouling. You could also hook 2 up so you have a back up if one were to fail(very unlikely). I just think the advantages of pulling waste from the bottom outweigh the far out chance that a pipe is going to burst or something like that. On a small tank with a low desnsity it might not matter but when you get into any tank with a relatively higher stocking density fish waste export is a big deal and something to think about when your design your water flow and drain outlet. A good indicator is that you should never see fish poop float in your tank.

I'm running some rather high density for Aquaponics and I haven't had solids building up in my fish tank. Actually, I have more problem with the solids building up if I only have a couple fish in the tank that don't stir it up.

And the magnetic reed switches, it is true that the actual switch is not exposed to the water so it won't be corroding, what can get fowled is the float that triggers the reed switch where something catches it and doesn't allow it to float down properly.

But to each one's own, at some point you have to choose where the risk is and deal with it.