LeighMo ) writes:
It's almost certainly that you don't have enough light. Cabomba
really
requires a well-lit tank.

That hasn't been my experience. My Cabomba actually grows bushier in
my
moderate-light tank, probably because it grows slower.

The original poster has 30W on a 15g, which sounds like pretty low
light to me. I don't know what kind of lighting is on your
"moderate-light" tank, but I suspect that it's much better-lit than
that.

Unfortunately, I don't know of any measurement that's both easy and
accurate for describing the light level in a tank. So your
moderate-light might be something that I would call a high-light.
Someone needs to mass-produce cheap underwater light meters to resolve
the problem. :-)

- Jim