pH levels for my 3 cichlids

Ok well for now I'm just going to use the 55 gallon until I move again. Then once I move and friend of mine and me are going to build a 300+ gallon aquarium so with one that big how many more cichlids would I be able to get or should I just stick with getting mates for the one's I have with one that big? Thanks for all the help again.
 
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