I don't know that it spreads just because I have had that happen to my mollie tank but it only happened to one of the fish. The rest are fine. I didn't treat with anything but maybe my other fish had better imune systems. Good luck!
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Tank: 75gal, 15gal LifeReef Sump, LifeReef Skimmer, 2 Koralia PH #2 and #3, 300w Heater, dual 175 mh with 2x 65 watt actinic, 74lbs LR Friends: Maroon Clown, False Perc Clown, Pajama Cardinal, Diamond Goby, Convict Tang, Starry Blenny, Watchman, Pistol Shrimp, Urchin, Sally Lightfoot, 2 Cleaner Shrimp Corals: Sun, Torch, Pipe Coral, Duncan, Galexia, Pulsing Xenia, Red, Blue, Superman, Ricordia Mushrooms, Finger Leather, Polyps, Toadstool, Flower Pot |