I bought a Co2 bottle,regulator and sil. from a friend who used for hydroponics.I think all I need is a bubble counter.Would adding this system be good for corals and fish or just the algae?*
Mg is correct: Co2, excluding use in a calcium reactor, is useless at best... it might give your undisirable algaes a boost, but it would be counter productive to your fish corals, and other livestock... you want o2 not Co2...
In a reef tank, we want to keep the pH around 8.3 and the alkalinity high. Injecting CO2 would make that quite difficult to maintain (outside its normal use in a calcium reactor set-up).
A calcium reactor can be a great addition to a reef tank. It depends on whether or not you have a need for one. If the calcium demand of your corals is high enough, investing in a calcium reactor can save you time and money (although saving money is more of a long term benefit).