Planted Tank Guru
Join Date: Jun 2004
Location: Baton Rouge, LA
That appears to be a submersed air pump, which can be hooked up to draw gas only from the DIY CO2 system; rather than plain air. Which sounds good in theory, but there's two problems:
1) The suction from the air pump may collapse the 2 liter bottles, causing yeast water to be pumped into the tank. Very bad.
2) CO2 will probably break down the rubber components in the air pump over time, causing it to fail.
So yes, get rid of the air pump. However, it sounds like you have another problem as well, since air and tank water was flowing *backwards* into your DIY system.
Make sure both check valves are installed in the proper direction. There's usually an arrow on the case, and it should be pointing in the intended direction of gas flow (away from the yeast bottles). If they're both correct, you probably have a leak.