Is it possible the old 10k's were so worn out the new 15k's were actually brighter and bumped up the growth?
Nope - the XM 10ks were probably about 3 months old. We may end up supplimenting the two 15ks down the road, as there is a darker spot in the middle of the tank (mainly due to that THICK centerbrace) but I've been keeping lower light corals there anyway, so it's no big deal. Just to give you a "for instance", a green cap in the RH side of the tank has put on about an inch of growth in about a month's time...acros are developing branches, and looked VERY happy (right up until the point the acro mites started ticking them off). We're doing the Interceptor treatment (da "stuff" is in the tank) so I suspect after the bugs are gone, the acros that are left will take off again. I'll keep ya'll posted on growth rate if you're interested. I don't get impressed "that" easily, and I'm VERY happy with these lights so far.

W.