Small Problem

What parameters do you test for? What do/did they come out as? Do you have any corals?

Did you test for phosphates and nitrates?

What kinds of algae?

If it green or cyano? Then cutting the light will hemlp. But if it diatomic, then you need to get rid of PO4 is your tank.

All kinds of algae feed on high NO3 level. Reducing this is a must.

With any kind of algae can be traced back to NO3 and PO4 and light.

Rohn

?? Do you have any fish? They probably won't enjoy having light for only 3-4 hours a day; corals especially won't.

Like has been pointed out already, there are a lot of kinds of algea and in saltwater tanks, there are algea 'phases' that are part of a cycle that continue long after the water is safe to keep fish in it.

Phosphates are a big reason why algea can thrive in a SW tank (and FW for that matter) and so it is something you should be testing for quite a big, IMO.

What sort of clean-up crew do you have? Many different snails will eat different types of algea and so it is best to keep a few of each, depending on tank size. Some crabs will also help out a lot like different types of hermits (I hear scarlete reef hermits are the best in most cases) and emerald (mythrax) crabs will help out with bubble algea quite a bit.

If the algea is on the glass, I found that all but a couple types are really easy to scrub off and even the harder types are easy to scrape off with a little bit of elbow grease. Inverts will clean off your rocks and so will some fish. I have a couple angelfish that really work on my live rock well and it is nearly spotless from the unwanted types of algea.

You should be fine turning the light off after 3 or 4 hours as long as you don't have corals. 3 to 4 hours a day of light is more than sufficient for fish provided the tank isn't in total darkness the rest of the time. Especially for short period of time till you get rid of the algae.

If you decide to scrap off the algae, don't clean you tank spotless of algae and this cause algae bloom after short period of time. Small amount of algae is important in reduing the nutrients in the tank.

Rohn