Several things to point out...
First, know your KH and set a target pH using the charts. Know what an optimum pH is for your KH and what is a dangerous pH. And be sure your test kit will read a pH at that level!
Then be sure to test the water frequently for the first few days adn observe the fish over that time, particularly in the morning. Note the pH as well as the bubble rate of the DIY unit. Keep that info. It is very handy to know that if you have x bubbles per minute that the pH is probably fine and if you have y bubbles per minute the pH is probably low and at z bubbles per minute the fish may be in distress.
Finally, if you KH is less than 3 or unstable, tending to fall to less than 3, DO NOT add CO2 until you have that stabelized!