Okay, and another question, one that kinda went unanswered earlier but I've partially solved.
I looked over some of Hoppys work again and reviewed this:
What this tells me is that if it sat directly on the glass in a 21" tall tank I'd have over 60 PAR, and without CO2 I read elsewhere here I'd be inviting Algae problems. So my question is what PAR is optimal to minimize algae while still getting good low-tech plant growth? This will allow my to figure out how high I want to raise the light.
OR, is simply running a light less than the usual 10-12 hours a day an option, or will that stunt the plants?