I have six cardnal tetras I just moved from a 20 gal tank with 8 glowlight tetras, 4 emerald cories. the water is 0 amonia, o nitrite, .25 nitrate Planted aquarium. PH is 7.4 temp is 78, and the cardnal tetras have small white spots on them and it looks like fin rot. any ideas on how to treat them? All the other fish appear fine, and the tank was set up in early december.