I didn't mean to imply that my fertilizer solution did anything for rainbowfish coloration or breeding display...which is what my "neon sign" comment referred to. I attributed their "happiness" to being in a healthy, thickly-planted tank.
Never had any dwarf neons (
M. praecox, right?) but I kept a few
M. boesemani,
M. herbertaxelrodi,
Glossolepis incisus, and a favorite from my last tank:
M.lacustris640x320.jpg
Melanotaenia lacustris (Turquoise Rainbow)
Unfortunately, I could never catch them in breeding display with my camera. The Turquoise was the most vivid with the stripe ranging from bright yellow at the nose, to orange, to white at the dorsal fin. He was the bully of the tank, too and was showing some aggression darkening in the attached photo. I tried to attach a photo of my
M. trifasciata one of his typical "yawning" displays but attachments aren't being kind to me today.