Just wanted to give my shout out to this Innovative Marine ATO unit. I think this is the best ATO setup you can build for less than $100. I currently have two Tunze Osmolators, one with optical sensor ($200) and one with a flow switch ($100). What I like about this unit is that for $70 you get a unit that is float switch free. Float witches are fine as long you regularly clean them. Any malfunction and you can have a disaster on your hands.

Since you can use any pump with this unit you can have a very nice ATO system for less than $100


Innovative Marine ATO unit with titanium electrodes - $70
Pump (I picked up a cheap pump from Amazon) $14
Some black acrylic tubing and elbows(AW and HD) - $8

Cost of a complete non-float switch ATO system - $92