PSA - Clean the sensor for your ATO!

Jamie9 · Apr 23, 2026

Just a reminder to clean the algae/gunk off your auto top off sensor if you haven't in a while!

I just went on a 10 day trip, happily the tank was totally fine when I returned. A couple days later and I woke up to the sound of falling water. My ATO sensor got covered in algae so that my tank level went down a fair amount over night. Happily no big deal as I was home...but if it had happened before my vacation...I would have come home to 25 gallons of very salty water in a 40 gallon tank!

Waters · Apr 23, 2026

Thanks for the reminder....I don't think I have ever cleaned any of my ATO sensors....ever lol.

Randy Holmes-Farley · Apr 23, 2026

FWIW, I had a similar experience recently. I cannot easily see into the last section of my sump since a minifridge sits on top of it for live phyto dosing. I have a little hole I can look through, and despite having warning signs of a low water level (lots of small bubbles in the tank) I could see the green light down on the Tunze sensor indicating all was well. Thus, i kept looking for other causes.

Finally I broke down and moved the fridge and other stuff in the way, to find the water level very low and the return pump sucking air. Cleaning the sensor solved the problem.

ColorMeGone · Apr 23, 2026

I clean mine once a week along with my wavemaker. It's a must do in my book!

mpatterson42 · Apr 23, 2026

Another thing to make sure you clean is your check valves on the return pipe (if you use them). I turned off my pump to do some maintenance in the sump, as I was looking at the sump I saw the water level was rising and rising and then the dreaded backflow noise, I suddenly realized I didn't hear the THUNK of the check valve when I turned off the pump. I quickly raised the nozzle above the water line to get it to stop. I removed the check valve and did a good cleaning. There wasn't a lot of gunk in there but I think just enough to prevent it from fully closing.

Normally my return nozzle is right at the water line but I had recently got an RFG nozzle and was playing around with different positions. I also took the time to drill in a small hole in the loc-line to act as a siphon break.