It's been a generally accepted credo that fish need to be kept outdoors to get sunlight to keep them black, at least until they become full grown. Many new owners of black fish excitedly bring them home and give them names like Shadow or Black Beauty, only to find their fish losing their black and turning orange or white.
Has this happened to you? Yes? Well, no more! Because from the laboratories of awrieger comes the solution to keep those black fish black! Heck, turn fish that aren't black, black!
Seriously though, this works. I've done it before, but now I know why. And it's absurdly simple. It's the light spectrum. More red and the fish's pigment increases. Don't believe me? Here's the calico ryukin I bought 8 weeks ago compared to now showing both sides:
The right side, 8 weeks ago, and now:
Excuse the more recent pics being more reddish, that's just the setting on my camera being different. Here's the left side:
I was actually concerned when I first got this fish (Johnson to his friends) because I could see the orange under the black on his fins and thought I'd lose the black. But no, it looks like the reverse is happening. And why? A simple red-spectrum GroLux plant growth light tube.
Now, I mentioned I had done this before. But back then I didn't know why it happened. I thought it might have been the pH. But now I know it's because this fish was in a planted tank which not one GroLux tube, but three! So the speed of blackening was vastly faster than my current fish. This fish went totally 100% black like a black moor within three weeks:
So there you go. No more 'oh why is my black fish losing it's black?' problems.