I have a stable, heavily planted 20 gallon tank with co2 injection and about 2.5 wpg. The tank is about 1.5 years old. Last week I added six new jumbo neons. The tank was home to three adolescent angels, two siamese algae eaters, and a couple of jumbo tetra.
About four days after the new tetras were added (sans quarantine, alas) the algae eaters and angels changed their behavior. They became sluggish, with the sae staying under the java ferns all day and the angels huddling together under the HOB water return.
Five days after the new tetras were added I noticed that four of the new tetras had disappeared, but I assumed they had been eaten by the angels. Then I found one of my mature tetras at the bottom of the tank and became really concerned.
Six days after the new tetras were added two of the angels were gone, with 2mm x 2mm whitish flakes of skin hanging off their mouths and patches on their fins. Now the third and final angel has the same on its side (see picture).
I'm running through a four day course of API E.M. Erythromycin, in the hopes that it will clear things up.
I've been testing my water almost daily, without any surprises. Ph is 7.4, Ammonia is 0, Nitrates and Nitrites are basically zero unless I fertilize (the plants take up everything I put in). Iron is barely measurable, so I don't think I overdid the trace elements.
Any comments or suggestions, even if it is just to tell me that I should have acted quicker (I was just too smug, because the tank has been so stable for so long...argh), would be appreciated.
Rich in Santa Cruz