i've heard:
- lighting
- flow
- placement
- livestock (clowns hosting)
each one of them has a plausible explanation, but, i still haven't come across anyone who has actually been able to PROVE that their theory is the right one. everyone just gives anecdotal evidences.
i have the nem from jesse in my frag tank, which has t5's and a MH. it hasn't really changed.
my DT has only LEDs..
but, if i put it into the DT, i wouldn't have proven that it was the lighting, since the flow is different, space constraints, etc.