I am currently running a primative DIY CO2 setup consisting of a 1.5l fizzy drinks bottle with a bulkhead connector to attach the length of co2 tubing - that leads to glass ceramic diffuser in the tank. This setup is working very well, although if anything, slightly too well. My 4dkh drop checker is yellow in the mornings, and slightly lime green at nights. Other than simply unscrewing the lid of the bottle at night, what can I do to regulate the co2 to the tank? I considered putting a flow restrictor in the line on that came with my air pump, but I don't want my rig to expode. I then thought about having a splitter; at night I could divert the co2 to just flow into the cabinet [a waste, I know, but I'm not too bothered] and then diverting it back into the tank by day. What solutions have others successfully employed?