A saltwater aquarium is a complex chemical system and its pretty much impossible to solve a question like this without more details about the system in question. Really, any attribute is an important part of the analysis--right down to equipment brands and techniques. Right now we don't even know how big the aquarium is or how its filtered.
Hi Ihave a 55gal Marinland filter its been set up 4 months red and brown algae. With small octopus not sure what type yet. Got it about a month ago,grayish with bumps on head. It eats beach crabs and sand fleas hermit crabs but not small shrimp whats up with that? It used my snail to prop up a rock now the snail is stuck and pushes the brittle star fish around I know I run lights too long. Try to cut back. What do you think about blue leds would still grow algae?
Sound like cyano and maybe diatoms. They often show up around 4-6 months. However, they may be due to a nutrient problem. I would test your water parameters and manually remove the cyano and algae/diatoms manually with a fine brine shrimp net or via siphon.
Which Marineland filter? Canister or hang on back? Either way, do you change the filter media regularly (and if so how often)?
LED's should result in less nuisance growth, however, if your nutrients are high and are causing the growth, you still have a problem you should address.
How often do you clean it? If you don't clean it regularly, you get nutrient build up and poor water quality. The mechanical filter doesn't remove goo, it just collects it, so you have to clean the mechanical filter and filter medium or the goo rots.