I have a 29 gallon tank that i got with an established blue gourami in it. Hes done well up until I put a few more neons in it the other day. Water tests out almost perfect and it started hanging out at the bottom (being almost lethargic). doesnt seem to be swimming quite right. only goes to top of tank to get a breath and then back to bottom. This morning I noticed a dark red spot looks like inside it. in front of side fins. any suggestions? all other fish seem to be fine and its never been bothered/stressed by other fish in there in the past.