Tunze Universal ATO & WC


New member
I've never used an ATO. So just a quick question. I do not have a sump, this is an all in one tank. So when I do water changes the water drops in the back chamber. So of course the ATO starts pumping water. I've been turning off the ATO to do the water change then turning it back on when I'm done. Even though the water is at the right level the ATO freaks out and starts pumping water, and not a small bit of water, almost a liter. Since by now I have figured it's going to do this I just let it fill up my bucket until it quits. The unit works perfectly otherwise. Does any one have a work around? Am I missing the obvious? Much thanks.


New member
I've always had my ato switches in the back chambers. When the pumps go off it fills it up and sets off the high level switch which tells my apex to turn the ato completely off


New member
The tunze pumps some water every time you cycle power to it. I wouldn't worry about it. Unless your tank is extremely small, the extra bit of water it pumps in will slowly evaporate and shouldn't cause any issues assuming there is room in the tank for it. I would say mine pumps for about 10 seconds on startup.


New member
You can change the flow rate so it doesn't pump as much in that 10 seconds after power on.
As mentioned, this is normal operation.


New member
Yes either turn down the flow on the unit or disconnect a single wire leading to the pump on each power cycle until the light goes green. This is a normal function for the tunze