fish turning black!

[kittyuk]

I changed about a tenth of the tank water two days ago (first ever change in tank set up for six weeks)
Two sunset gouramis are darting along the back ever since, and their fins have a black look to them. The fish are eating. Now I notice the silver mollies are getting a slight black tinge to the top fin. I put water conditioner in the new water, but added no extra salt.
Any advice?

 

[William]

Right well, do you have test kits for ammonia and nitrIte that could help a bit in determining the problem. The fins going black is odd, I can't think of anything which could cause this although I know that there is a disease called "black spot", that would be spots and not the whole fin.

Are you sure its not just the lighting? The fact you added no extra salt should be no problem and just 10% change of the water is unlikely to have damaged anything in there, did you clean the filter?

Look forward to hearing from ya and good luck!

 

[kittyuk]

Thanks for the reply, William.
The filter is an undergravel one. When I rang the lfs I got the fish from, they seemed to think it is stress, and they aren't worried because the fish are eating. We got the two affected gourami three days ago, and they were perfect, swimming together, until I changed the water the following morning!
The fish were a lovely yellow and blush colour with clear fins, edged with lemon, but now the fish look grubby and their fins are darker.
The lfs suggested 'stress coat'.