About a two weeks ago I started my saltwater tank. I have only had the water and today I will get the live rock. I want to know if the PH makes a difference with keeping fish. I know that PH makes a big diff. but I want to know if I can keep several diffrent type of fish in the same tank without worrying that they will get sick because the PH level is not right for them or do most fish sold in pets tores live withing the same PH levels? I plan to only keep it with live rock and fish for know but if I change my mind later and want corals then will it make a big difference?