04-29-2013, 02:21 PM
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I concur with what's been suggested. As someone who has had this very same problem, I may be able to add a bit.
Tank-raised fish (which angelfish will be unless you deal with a direct importer of wild fish--but the Black Lace is a tank-bred variant so not wild anyway) seem to be carrying more and more pathogen, especially internal protozoan, these days. I now quarantine all new fish for 5-6 weeks, since I lost about 1/3 of my main tank a couple years ago. Melafix and similar products will not help if the issue is internal protozoan.
Adding two angelfish to an established tank should not in itself have caused any ammonia or nitrite issues. But there was the recent make-over with new substrate (even if done in stages). Are there live plants? Floating plants (which angelfish like on their own) will help a lot when it comes to nitrification, and issues with minor problems are easily handled.
Another issue that occurs to me is adding angelfish to an existing shoal. This is never a good idea. The existing group will have their hierarchy within the group, and any newcomers will almost always be seen as intruders. Some suggest moving the existing fish to a new environment when adding new fish can get around this, and sometimes it does, but sometimes not. Once a group of angels is in a tank, leave them. The additional stress of this aggression, on top of the considerable stress of moving the new angels to this different environment, plus any of the other issues...pretty soon it is a considerable stress load and this will cause some health issues that might perhaps have been fought off otherwise.
As trouble is still present (the behaviour of the angelfish) I second doing daily water changes of half the tank, using Prime but not more than needed. I assume the nitrates are not in the source (tap) water? Water changes should get these down, which is important. Vacuum the substrate too, as suggested earlier by someone.
Last edited by Byron; 04-29-2013 at 02:25 PM..