All my leathers are under 400W MH (10K) and doing just fine - full PE, puffed up, no bleaching or signs of distress. I brought home a HUGE colt the other day and it seems to be thriving under MH with lots of (random) flow. Leathers are pretty easy going corals - as long as they're acclimated to changes in lighting or water parameters, they'll thrive in all sorts of conditions.