Angelfish have damaged fins after transfer
I have had 4 angelfish in my 100 liter aquarium for a week.
this will not be successful in the long term! Just 2 angelfish already require at least 200 liters; permanently keeping 4 specimens is possible only in more than 500 liters. At the latest when two fish became mature and formed a pair, the other ones will become certain death candidates. Furthermore, a 100 liter tank simply does not provide enough space for these rather big fish!
But just one day after the purchase I noticed that the "skin" of the dorsal fin disappears and only "bones" stick out like needles. It would be nice if you could tell me how I can heal this without further remedies.
These symptoms sometimes occur when the fish are transferred into water with considerably lower salinity than before. Due to osmosis, more water gets into the cells which can in extreme cases burst. It has even been observed that fins were actually divulsed (please see the sera guide "Healthy aquarium fish", section "osmotic shock"; available for free in the download section)!
You can add sera mineral salt as an immediate measure; a mild anti-bacterial additive (sera baktopur) is also very advisable as to prevent secondary infections. Generally, adaptation from high conductivity water to water with lower conductivity must be carried out with much more care than the other way round!
Edges of the affected skin appearing slimy and opaque are usually caused by bacterial fin rot. In such cases, treatment is possible with sera baktopur direct, furthermore the water hygiene should be checked and optimized if necessary.
Dr. Bodo Schnell