Top fin of two rosey barbs turning black. h-e-l-p

[itswoodie]

Hey guys/gals,
Been about a week or so since I posted on here. My new 20 gal fresh water is going well. Except for this one problem.

I have four rosey barbs in this tank. Two of them are yellow, and two of them are bright pink. They've all been in there for about a week and a half now... Anyway, I just noticed the other day that the top fins on both of the pink roseys are turning black.

After careful inspection, I can say with certainty that its only these two fish that are turning black. What in god's name could it be?? I've been doing regular water changes, not overfeeding, and monitoring their health (they are both very active and 'carefree').

I googled it, and couldnt find any decent info. You guys have any idea what it could be? Thanks in advance :bowing:


-wood

 

[Blinky]

Could you post a picture, or try to give a really detailed explanation of the colouration? There are diseases that cause fish to turn black, but it may also be the fishes' normal colouration - I have never kept rosey barbs, so I don't know off hand if this is normal for them. If it looks exactly the same on both fish and they appear happy and healthy, I'd suspect it's nothing to worry about.
If you think it may be disease related, can you post all your specs, water test results, etc. as that will help others to pinpoint any problems.

[edit] I just looked up rosy barbs, do they look like this picture? http://images.google.ca/images?q=tbn:D_1-PgQs3f0J:http://www.****************/images_01/rosy It sounds like you have two males and two females, and this colouration is normal for males
This is from www.liveaquaria.com (a site that popped up in my image search): "The Rosy Barb is one of the larger Barbs that can grow up to 6 inches in the wild. The male is red and gold with black spots near the rear and at the dorsal fin. The female lacks the red color and is mostly golden."
[/edit]