How many gph for a powerhead for a 75 gallon?

[Makubex]

Currently using a sunsun uv sterilizer which moves a bit of water inside and a cheap $12 small powerhead, fully stocked some corals such as mushrooms

 

[Sarlindescent]

There are multiple factor, such as rock layout and coral type. For a softy/lps tank, you can get buy with 10-30x turnover. For SPS, some have over 100x turnover. So for a 75, you could use as little as 750 gph and potentially over 7500gph. If you intend to stick with mushrooms, 10-20x is good.

On the pump side of rock, there will be high flow and on the backside of rocks, nearly stagnant. Because of this, it is recommended to have at least 2 pumps. Running higher power pumps at lower speeds generally nets quieter performance.