It sounds like you might already have an understanding of what happened, but just to be sure, let's walk through this:
- CO2 goes into the water from the CO2 tank, and the reactor helpes the CO2 dissolve in the water so less escapes from the tank.
- Excess CO2 in the water that isn't absorbed by plants has a tendency to react with the water and form carbonic acid (H2CO3).
- This build up of acid will lower the pH in your tank, and in large enough quantities, kill your fish.
So, what you need to to do is find a way to regulate the amount of CO2
that's going into your water. That's where the solenoid valve comes in - when attached to the regulator, it makes it much, MUCH easier to fine-tune the amount of CO2
going into your tank.
Side note: you may want to look up how much CO2
you should be releasing into your tank (as measured by the new bubble counter you'll be getting). This amount will vary with the size of your tank and the amount of plant matter available in your tank to process this CO2
As for the reactor itself and the aesthetics of your tank - what kind of filter are you using? I may be wrong, but I think the Serra 500 is an in-line CO2
reactor - that means it can be stitched into the output hose of a canister filter. Attaching it to a powerhead sounds like it could work, but I'm not familiar with using one of these diffusers in such a way.