What size tank is it on, Carlo? The 37g or 10g? And what is your CO2 setup (1 bottle, 2?)?
Generally, DIY CO2 will not produce too much CO2 to where it will hurt the fish. If you had some insane setup of like 5 2L bottles on a 10g, well that might do it though.
1 or 2 2L bottles on a 10g won't hurt though.
Look at your fish.....are they gasping at the top or anything? If so, then its too much CO2. Otherwise, if they are fine, your CO2 is fine.