Fropm what I've read, I think the wrasse may be too large for this tank but Im sure the firefish will make a wonderful addition to it as they can go in tanks down to 10 or 15G. this is of course depending on what is already stocked in your tank with the bioload question, I would agree that understocking is the way too go in marine as, the more fish, the bigger the amount of ammonia and hence the bigger the load and may create more nitrates than your phosphate/nitrate remover can handle. And as we know, nitrates=bad in marine so understocked is better than even a medium stocking IMO