I use a venturi diffuser with DIY CO2. The powerhead is on the same timer as the lights but the CO2 injection can't be turned off like pressurized CO2. Its been 1 1/2 hours since lights and powerhead went off but the pH has not moved from the 6.4 range. Am I too impatient with degassing or is CO2 still dissolving into my water at a rather fast rate. The CO2 is coming out of the burp tube right now since the diffuser container has filled up with a nice pocket of gas. The only source of surface disturbance in my 29 gallon is my penguin biowheel 200 filter. Should I run an airstone after lights out to aid in degassing the water or will it naturally degas on its own at night without subjecting the fish to 24/7 high CO2 levels.

Ask yourself this, is the CO2 dissolving when the powerhead is off?
The DIY CO2 will still go into the reactor, but it'll simply escape out the burp tube.

When the powerhead is on, the reactor will start dissolving CO2.
You can also set a timer for the CO2 to come on 30 min prior to lights on and 1-2 hour or so before they go out.

Regards,
Tom Barr

I tested the pH this morning 30 minutes before lights on (and powerhead on) and the pH only moved up 0.1 so I have decided to put an airstone on a timer that will switch on for about 4 hours after lights out in order to degass the CO2. Many of you have done this without any fish harm so I might as well do it also. I just don't like the idea of high CO2 concentrations (30 ppm+) at night when the plants aren't using it.

How can CO2 remain 30ppm all night long?

Think about that.
Adding some more surface turbulance will take care of that, but what you are suggesting is that the CO2 level takes over 12 hours to degas and even then, that barely puts a dent in the CO2.

I doubt that's what is going on.
Increase the surface turbulance some, don't worry about it.


Regards
Tom Barr