"Problem" algae - algae that grows faster than it can be managed is generally caused by

Brown algae growing on rocks

My tank is about 4 months old and I am noticing a brown like growth on my rocks.
I don't know if this because I use sea water from our local aquarium and store it in clear 5 gallon. containers.
I am considering switching back to salt mix ....the way i started my tank

Algae will grow and you should have a management team of herbivores in the tank to help keep that in check. Blue legged and scarlet hermit crabs help allot with algae as do herbivorous fish and the snails.

"Problem" algae - algae that grows faster than it can be managed is generally caused by

Un filter tap water (non ro/di water)
Incorrect or old lighting (lamps that have out lived their usefulness generally + 6 months old)
Over feeding
Low calcium levels