chemi clean? what's that do? I'm really worried about adding chemicals to my tank since I have heard so many stories about them wiping out peoples inverts and corals.

the lights were on a good 12-13hours (both on)....one phased in 30mins before the other (ex: on 7AM then on 7:30AM) then off 30mins before the other (ex: off 8:30PM then off 9PM)....I didn't know you could have too much photo period?