Well, its difficult to control the flow of CO2 when you have a DIY setup. I would say that you should probably figure out a way to diffuse less of the CO2. For example, instead of hooking it up to a diffuser thats going to make fine bubbles, I would maybe let it run on something thats going to give off larger bubbles and have quicker access out of your tank. Then you can adjust accordingly. On my 37 Gallon I had DIY pushing full size bubbles into a CO2 ladder. As the bubbles travelled up the ladder, it would diffuse into the water due to it having longer contact with the water before the bubbles were released to float to the top. I had a pretty high CO2 concentration that way.