I also worked on my aerator timer control. I built it from an arduino pro mini, relay board, and re-purposed car charger. The original timer doesn't work any more and a new one is $40. I had this stuff already and all I needed to do is write the code for the board to work its magic. 3 selections: 1- aerator on 1 minute off 10, 2- on 1 minute off 7, 3- on 1 minute off 5. This will keep different amounts of fish alive by supplying them with fresh water. Ex: 5 fish will not need fresh water as often as 30 fish.
I actually didn't write the code. I wanted to learn how but a guy posted an awesome sketch that works just as intended.