I'm sure this question has come up before and I am sorry if it's repetitive but I've been doing research and not sure if it's stress or normal. I have a discus (not sure of the type) which is about 6". I've had him for about a year now and I keep him with a number of other smaller discus(he's def. the biggest in the tank). Up until about 2 days ago he was bright yellow in the body, his fins are red with the blue patterning and some more blue on the face, recently his body has started turning a dark red and the blue patterning seems to be covering almost his entire body. There's some yellow around the face but it's very faint now. I've been seeing that when they turn dark it usually means stress or a parasite. I'm not sure how "dark" is really defined and this strikes me more as a coloration "change" rather than stress. I've always heard they as they grow their colors change so made it's a result of that. Everyone seems happy and healthy and eating well with no issues. I've been testing the water and all's well. The only thing I've changed lately is I've started adding about 1/3 the recommended dose of "blackwater" treatment to replenish lost minerals after my RO filter. any thoughts?