Please help i'm worried about my porcupine puffer i've recently started my new hobby of marine fish keeping and after a month of letting my filters mature i,ve purchased some fish I have two sand sifter star fish a brittle star fish a coral beauty and also Spike a porcupine puffer the problem is he is nearly always hiding underneath rocks or behind rocks is this normal behaviour for puffers or is there something i should worry about my other fish are perfectly fine they swim about readily eating well my puffer eats well at the moment just feeding him whole shrimp water temperature is fine within the green on my thermometer salinity fine nitrates within the right range ammonia great been told by the shop where i bought him that he may be bothered by the coral beauty but whenever i see them my coral beauty goes no where near him