Brown slimey algae isnot good. It may be dinoflagellates or snot algae. Here is an excerpt from the algae control page jere on our very own web site.
"Dinoflagellates (brown slime, snot algae)
Dinoflagellates are closely related to the endosymbiotic algae in our inverts; zooxanthellae. It is called snot algae because it has the consistency of nasal mucus; it is transparent to brown in color. It lays down stringy sheets, similar to Cyanobacteria, which trap air bubbles in their tissue. This is a very dangerous alga because it has the ability to quickly remove oxygen from your system. It has also been hypothesized that the algae is toxic to herbivorous fish and snails. The treatment is much the same as Cyanobacteria, with an addition, try to keep you ph
elevated above 8.6 during the day and above 8.3 at night and you should see it crash pretty quickly."
Try to get this under control as quickly as possible.