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Auto Top Off

Jan 4, 2006
Who here uses an auto top off unit?

Does anyone have any plans that they can post?

Which work best? Electronic? float valve w/o metal? or ol' tube in a sealed container?

I want to make one elevated above my sump (under the tank) and am looking for input.

Thanks Everyone!!
There is a good illustrated set of instructions at floatswitches.net.

Mine is nearly identical to the one they spell out there with two switches in series controlling a solenoid (whatever you do, you don't want to send 120 V AC into your float switches!)

Mine differs from theirs in a few aspects. First, there are a few out there who think that just having two float switches (one controlling the level, and one above it as a backup should the lower one fail open) still isn't enough safeguard. I address this problem by using a very low-flow dosing pump (a $10 aqualifter flapper pump) hooked to a timer. Basically, the top-off unit is only active for about a half hour a day. That way if both float switches or the solenoid were to fail open, it still wouldn't flood. The other thing I did different was I soldered most of the connections, and used a piece of 2" PVC with caps on either side as a housing for the solenoid and connectors. A slot in one cap allows the wires to come out, then its all siliconed to heck.


I am going on vacation in a couple of weeks and am considering whether to splurge and buy a premade auto top off, or try and DIY. I have rewired a lamp before and installed a garbage disposal, do you think I would be able to do it myself? Oh, and don't ask if my hubby can help :roll:, he isn't allowed to touch any tools in the house, he has NO mechanical ability... he's a great musician, just not so talented at fixing things.
I cant see having a tank without an auto-top off.

Again, theres many ways you can do it. For years, I didnt use a resevoir. I have the rodi unit hooked straight to a float valve in my sump. Very simple and never failed in any way. My current setup is still under construction. I will have a 20 gallon reservoir where the rodi will goto a float valve. I will also have the float valve goto the sump. From the resevoir, I will add kalk or salt or anything I ever need and have a dosing pump slowly pump this into my sump. I will keep the dosing pump set to a speed slower then my evaporation rate, and the rodi will match whatever more water is required to reach the correct water level. Ive never really felt the need to use a float switch (electronic) for auito-topoff. But I do use one in a 5 gallon bucket that catches my skimmer water that goes through the collection cup. When the bucket is full, the switch shuts off the skimmer. Since the bucket is 5 gallons, I know exactly how much salt I need to put back in the system.

If I had more room..I would have another container such as a 50 gallon drum. Have this filled with salt water. And have two pumps on timers go on for a small amount a day. One pump to take water out of the main tank and one pump to pump new salt water from the drum to the tank. It would be like an automatic mini water changes!

cuttlegirl-DIY float switches arent too hard, But you can also just buy ones from autotopoff.com. I believe thales suggested that site to me a whole back.

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