Algae Problems - looking for some help

[IJC]

Like I said, there've been some snail deaths, but that's it.

My system is:
54 gal,
20 gal sump
Lots of live rock in the tank, and additional base rock in the sump
Berlin Turbo skimmer in the sump
250watt iwasaki and two VHO actinics
Laguna 7 main pump, 2 802 powerheads.

1 medium yellow tang
1 small clown
2 chromis
1 6-line wrasse

Quite a few different corals - sps, lps, and softies.

A whole bunch of macro that I can't keep ahead of.

Water changes are monthly, 15 gallons.