Well, I have a 75 gallon saltwater tank. It's been running for almost 5 months. I've been have a brown algae problem for about a month, and get get rid of it. "All" my test read back right around where they should, and I do a water change every week.
I'm running a canister filter, a UV
light, protein skimmer, and a small hangon filter just for extra filtration. I also have a power head for water circulation.
I've have another saltwater tank for years but never had this problem.