derbesia algae outbreak

Hi folks;

I've had my marine tank set up for about six months. 55gal, Remora HOB
skimmer, 67 lbs live rock, 260w lighting (50/50 blue actinic/10000K), two
MaxiJet 1200 powerheads, two inch aragonite reef sand layer. One sailfin
tang, one maroon clownfish, one engineer goby, two bubbletip anemones (was
one anemone until it split last week). Five turbo snails and a red-legged
hermit crab. 5% water changes with RO/DI water (Spectrapure MPDI-25) once a
week. Temp 76-79F, pH 7.9-8.2, s.g. 1.025. No detectable phosphates, 1 ppm
nitrate (Salifert kits). I've been using the Spectrapure unit for about two
months; before that I was using an Aquarium Pharmaceuticals Tap Water
Filter.

Over the last month or so I've had real troubles with derbesia algae. I
suction as much as I can out with my water changes, but it just comes back.
It's growing along the back glass and is covering at least 80% of the live
rock surface. Now it appears to be growing in places on the sand.

My live rock is anchored down with PVC piping and ties, so I'd rather not
take it out to scrub it by hand. What course of action should I follow to
get rid of the derbesia?

I've been thinking about using a waterpump and suctioning the water through
a fine mesh media bag and back into the tank, in order to trap the algae in
the bag and remove it, but have been told that small amounts of the algae
will get back into the tank in the form of smaller particles (?), making the
situation worse.

I've also considered increasing the frequency of my water changes,
suctioning out the algae as I've doing during my weekly water changes, but
am concerned about stressing the fish.

Any advice? Thanks in advance.