I use 4 bottles on my 80gallon, lasts 6 to 7 days, i change them even if they are still pumping co2, i use to leave them and got bba. My water level touches the the rim of my hob so i have very little surface movement. when i do a 50% water change and add my new co2 bottles i get pearling every time - new minerals and salts. I would not remove bio wheels - but i would not feed co2 into the intake of the hob either, you loose most of it.