I have a 29 gallon tank with 0 nitrites, 5 nitrates 0 ammonia. Filter is a 50 gallon capacity hob. I have a single baby convict cichlid in it with some plants and activated carbon. I have been advised to put 15 ml aquarium salt in my tank for 3 days, but after the second day, my fish is gasping for air! He js getting paler and the area around (but not inside) his gills ks getting even more pale. Help!