05-20-2011, 11:22 AM
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Zof was spot on, it's flashing.
Check ammonia and nitrite levels just in case. But more likely it is parasitic. Ich is a parasite, the most common, velvet is another sometimes encountered especially with certain species (and much harder to deal with).
Ich occurs in all natural waters, and fish build up a sort of immunity by secreting more mucus (the "slime coat" we refer to) which repels the parasite. However, it (ich) always first attacks gills, and that is why the fish "flash", they are trying to dislodge the parasite from their gills.
If the fish are relatively free of stress, in a clean, healthy environment, this will pass and not worsen. But if the fish are stressed by inappropriate environment, water conditions, "bully" fish, temperature changes, etc., the ich will reappear and can worsen to the point of the visible external spots. Some form of treatment may then be needed, depending upon several factors I won't go into now.
I see this periodically, the flashing I mean, and I leave it alone. With a clean environment it clears up without treatment. Keep an eye on the fish, and maintain good water quality, and feed nutritious foods. Avoid any stress as much as possible. Jumping to any treatment adds further stress on all fish in the aquairum, and this can actually make ich worse and spread it to otherwise healthy fish, so it is preferable to deal with it naturally.