i have 1500 GPH
in my 35 gallon, one of my koralia Evos impeller shaft seased up so since i have to replace it i'm going to buy two evo 750 impellers to replace the 550s bumping my GPH
to almost 2000.
if you're going to go with a reef setup aim for about 30x the total volume of the tanks flow so for that 75g i would go with atleast 2500, if you want SPS
corals then try and hit 50x the volume or more.
you can never really have to much flow fish will be happy with whatever they are in as long as they aren't plastered against the glass