Discus fish gone dark! Need help :(

[TomCarter13]

I went to a pet shop a few days ago and bought my first 4 discus. When i went into the store there were 2 that were literally black (brilliant turquoise discus) and 2 that were colourful and happy swimming around (pigeon blood and marlboro). I knew that dark discus are bad signs but when the lady fished out the other 2, the other fish flared up and lit up and were so beautiful! I had to get them! They still have bright colours on their fins but they are still dark in the centre i've just done a water change to see if it would do any good so im hoping but can anyone help me or give me advise?

Here are the fish looking the best ive seen them

 

[TomCarter13]

Also the water parameters are:
Ph: 7.3-7.4
Am: 0 ppm
Nitra: 5 ppm
Nitri: 0 ppm

 

[Delapool]

Really need a discus keeper here as I've never kept them. Ammonia looks good so apart from clean water and pwc's i can't think of anything else. How are they doing?

 

[TomCarter13]

Well they are all eating and the largest one has coloured up very well and is eating and also being aggresive when eating which is a good sign. The other one is still dark but has improved since i made this topic. He eats really well and they all come up to the tank when im around now but the largest one is really aggressive and i think its because he's alot bigger than all of them. He's dominant and the others are Submissive. The larger one ALWAYS harasses the other dark one and i think that's where the stress is coming from?
So i might have to return a/some fish

 

[Delapool]

Well they look good. Almost converted to discus on the spot

So why is a dark fish bad can I ask? Just out of interest.

 

[TomCarter13]

Hahaha yeah they're getting better by the day but like i said the two that i was worried about are sooo so aggressive.

A Dark discus is just a signal that something's wrong. Whether its bad water quality, sick, or even just stressed the darkness could mean alot but my water quality was fine and they weren't showing symptoms of any sickness but i'm now going with the fact that they were both stressed

 

[Delapool]

Thanks, handy to know. Good luck with them