Why does my live rock look greenish brown?

[gsumner2]

I think I have some kind of algae bloom that I really don't want! I have a 55 gal with 30 gal refugium. The tank is 6 mo. old and was doing great. But I just upgraded to a new light fixture with 2 250 watt metal halides and 4 actinic white and blue/moon lights.

My tank is overstocked on fish and I have already ordered a 180 gal. tank that I will be moving stock to in the next month. I test at least once per week. So far ammonia- 0 nitrites- 0 but nitrates 40. I have been doing a 20% water change monthly. My refugium and a some grass/macroalgae in the tank seemed to have red slime, so I treated for that a few days ago and did another 20% water change - not all of the slime disappeared like it did one other time, so I think I may have something new.

The water looks clear and the corals but everthing else in the tank looks like it has green/brown stuff growing on it.
Please Help!:eek2:

 

[sir_dudeguy]

well you didnt really describe the alga that is growing (is it really thick slime? Is it just hair alga???) but high nitrates would be the cause of most.

I suggest doing a water change every week or every other week.

 

[Snowboarda42]

check your phosphates too, they will fuel algae.

 

[gsumner2]

The algae is a brown color and it coats some spiky sea grass I have growing on a rock, some red macroalgae and some halimeda catus macroalgae. Some recent live rock has small bubbles and more of a bright green growing on it.

How do I control this undesires algae? Also, besides water changes, is there another way to lower nitrates? My refugium has miracle mud with 6 red mangrove plants growing in it. The problem algae is also growing on them and the refugium sides.

Thanks for any help.