Please HELP Discus in pain

[Azz]

Please help me, I have 7 discus, 3x Red Turks, 2x Snakeskin and 2x Cobalt Blues they are about 3 inches.
I am very concerned because three of my discus keep going dark and when I go close to the tank they start to go back to their usual colours and its been happening for the past 4 days. I can’t identify any diseases because they don’t hide, they are swimming fine and eating well and they have their fins up almost all the time.( in other words perfectly happy) The tank is planted-out sparingly. The discus’ tank mates are a few angels, 3 clown loaches, bristle nose pleco and two corys. I was advised to put cory’s in the tank because I heard that if they ever go up to the surface of the tank there is a problem with the water chemistry. But the cory’s have not been to the surface which I believe means the water chemistry is right. My water temp is stabilized at 30 degrees Celsius. My fish have been settled and happy without any probs for the past 4-5 months until now. The fish are well fed on frozen bloodworms and tetra prima discus granules. If anybody out there could help me or advise me on what to do I would really appreciate it. Thank you for your time.

The PH is: 5.5
Nitrate: 5
Ammonia: 0
Nitrite: 0.1
Please Help

Thanks for your time

 

[sphed]

If they are all eating they are probably fine. I would just increase your water changes and play it by ear.

 

[Azz]

Thanx for your reply, I just done a 25% water change, I guess i'll have to wait now.

 

[Dan Steveo]

if they are dark before you walk up to the tank then maybe that is their true colour but when you get close the get slightly scared and go paler.... does this seem right or do they go a different kind of dark?

 

[TheFool]

I wouldn't worry if your cories ever go to the surface. Rather like anabantoids, cories need to go to the surface every now and again to breathe a little. It's anability they have to survive in very warm water, and for most cories, 30 C rates as rather warm.

How big is the tank by the way?