bala shark losing black colour

[renee]

Hi I have 2 bala sharks about 5cm long I have noticed that one of them keeps losing its black colour on its fins then gets it back and so on. I was wondering if any one knows why? They don't look sick they are eating normally. They are in my tank with some guppies

 

[CAPSLOCK]

Are they doing it at a certain time? Like after lights out, if they are startled, if you move stuff around in the tank and they hide? A lot of fish will lose color or vibrancy at night or in response to stress.

Also what size tank are they in? Balas get pretty large and active so they need a lot of space. Not sure if crowding would also affect their color.

 

[arcab4]

correct me if i'm wrong..but i think i remember reading that color changes can be related to water quality. and like capslock says...stress too. knowing the tank size and how long it's been setup will also help out trying to find a solution.