75g is one of the best sizes out there. It allows you to do so much with it and not overcrowd it. A fahaka puffer wouldnt really work in a 55. Puffers get bored very easily and that leads to nipping and eating other fish. If you want puffers though amazon/bumblebee puffers can be in a group and get along with other fish. Very personable puffer but they can get fat quick due to them always acting like they're never feed. Dont fall their cute little faces. Green spotted puffers are great too and a 55 would be perfect for them but they get to be high end brackish to low marine salinity after a while. But it's really not too bad I still use a sponge filter for them and it's good. Oh and dont forget about snails along with other crunchy foods because of their beak