A caution on adding CO2...this is not really beneficial except in high-tech planted systems where the plants are the main focus and fish are few if not altogether absent. Natural CO2 occurs from the decomposition of organics in the substrate primarily, and there is quite a lot of it. Depends upon the plant design you want. There is evidence now that diffused CO2 does affect fish, and the so-called liquid carbon supplements can be deadly to plants, fish and bacteria.
This also means you can lessen the light intensity, which further benefits the fish; most of our fish are forest fish that live in fairly dim waters, and overhead lighting does impact their lives more than we might expect.
This also means you can lessen the light intensity, which further benefits the fish; most of our fish are forest fish that live in fairly dim waters, and overhead lighting does impact their lives more than we might expect.