Utube DIY CO2 thats what i did they have step by step instructions.
Thanks for the info, it is very useful.As for at night, you can turn the power head off (i.e. put it on a timer) so that the CO2 is not efficiently diffused. As additional insurance, you can also add an air pump and airstone to create more surface agitation at night, which will increase gas exchange (an airstone does not introduce oxygen into the water directly).