One Of My Corys Is Darker Than The Others

[aquadude]

Hey guys. I have three emerald green corys in my 29g tank. I am new to the hobby, and was told by my local Petco that I wouldn't need to go through the cycling process, and thus added these fish to my tank a few days after setting it up. I added those fish about three weeks ago. I have since decided, based on research and the advice of others on this forum, to cycle my tank. One of my corys looks noticably darker than my other two. I have just noticed this in the last few days. I'm not sure if he/she was always like this, but he also seems a little less active than the others the past few days. He eats and still swims around with them, but sometimes they will be zipping around the tank, and he will be sitting in a corner by himself. He doesn't appear to have any fungus or growths on him. Anyone have any idea if anything might be wrong with him? I will try to post some pictures in a bit

 

[Harlequins]

What is your water stats for ammonia/nitrite,nitrate, ph, & temperature?

Could be its colouring although may be an infection brought on by poor water quality...

Depending on your readings you may need to do waterchanges to start with,

 

[aquadude]

Yeah I've started to change the water more, since the ammonia is around .5ppm right now. Doing a 5 gallon change daily for the last few days, until the ammonia goes down

 

[Harlequins]

I would up your waterchanges to 50% daily,you have a plec also? the plec with affect your tank because they are poo machines,

Whats your readings for nitrite?

 

[aquadude]

Nitrite readings are zero... I will up the water changes to 50% and continue to test daily. Thanks for your advice.