Earlier today in an unrelated post I mentioned how my Danios rub themselves on things (driftwood, sand), escapay commented that it could be something worth keeping an eye on. I've observed that the main culprit is a male Leopard Danio. I've also noticed that he is looking very stressed, ie, pale gold, spots very faded. They all lost a bit of their colour after the major tank re-scape I did the other day, but their colours all returned within an hour of being back home... Except for this guy. Coincidentally, this is the same fish I've recently commented on being particularly aggressive towards nearly everyone else in the tank. I've just tested their water(API Master): temp-21c, PH-7.4, Ammonia-slightly above 0, below 0.25, Nitrite-0, Nitrate-10. Is this behaviour, and lack of colour, anything to worry about, or would it just be regular doctors advice of keeping an eye on it and noting if it changes?