Rather than deal with soldering wires and losing tank space with floating switches, or pay top dollar for an ATO controller, I decided to engineer a simple time-based ATO system.

Hardware Required:
1. Small fountain pump (I used a Tom aquarium aqua lifter. ~$10)
2. Digital on/off timer ($10 from home depot)
3. Airline tubing
4. Check Valve
5. Water reservoir (I used a 1 gallon plastic container from K-mart, $2
6. Aquarium sealant.

Poke two holes large enough for the airline tubing in the top of the gallon container (not the lid). One piece of tubing ~3 inches is inserted in one of the holes, with equal amounts of tubing on each side of the hole. Seal the tubing in the hold with sealant (this is for venting purposes. I felt the tube would prevent debris from contaminating the reservoir, but you could omit this step if you prefer). Through the other hole, run tubing to the bottom of the reservoir and then to the inlet port of the pump. Connect a piece of tubing from the outlet port of the pump up to your tank. I connected the tubing up the back of the tank with suction cups, curled the tubing over the rim of the tank, and then held it in place with one more suction cup on the interior of the tank. Plug the pump into your timer.

I observed that my 4g pico tank needed topped off with about a quart of water per day. The pump claims a flow rate of 3.5 gph. After a little math, I calculated that a two minute fill 2x/day would equal just about 1 quart.

So far this system is working out nicely. I realize that evaporation rates vary depending on the ambient conditions, so this set-up with require a little monitoring to make sure that the levels stay constant. Tinkering with how long you run the pump can easily correct this.

I like this system for the ease of setup, and not having a float switch taking up space in an already crowded pico tank. Let me know what you think. I'll post pics later tonight. Thanks.

Can you post a picture of your set-up?

While it is simple, it's not nearly as accurate as a float switch. Evaporation rates can change daily in certain areas of the country, and will change greatly now that the weather is warming up. A float based ATO isn't that hard or expensive. You're spending about as much right now. Swap that timer out for a float and you are basically there.

Ask and ye shall receive.

Click to view attachment


Again, I realize that this set-up isn't as accurate as a float switch. However, in my climate controlled condo, the evaporation rate has been very consistent, and I'll sacrifice a little accuracy for the aesthetics of not having a float switch in a small tank.

Is that tabletop waterproof?

this is exactly what i do, the problem comes when i accidently leave part of the lid open or something

What problem does that cause?

Changes the evaporation rate. When you turn your AC on in the summer, it will also change the evap rate. So will air movement in the room, relative humidity, etc...

if you have a lid on your tank I think it will be more consistant, but if its open top, it could be way different as the seasons change. It will work fine as long as you check salinity every week or so I think.