A little update. Went on a little vacation to see our son in Japan before the holidays. ATO decided to stop working. The guy taking care of the tank says "it looks like your fish are swimming in snow". He was kind enough to go back, only lives a few blocks away, he ended up having to topoff the tank manually, daily. I asked him if he just noticed it, he was like, nah, was like that yesterday. Lost 10 nice frags thus far
I have a Tunze 3155. I guess there was some buildup on the sensor. I just wiped it off when I got home and it's been working ever since. Probably tells you in the instructions somewhere about periodic maintenance. Who reads that stuff. LOL