Hello there, don't visit often but decades of experience.

First, no tank should ever be by a direct sunlight window (you didn't say if filtered or direct so just tossing this out). With such a small tank not only algae but temp swings or overheating are dangerous possibilities.

A plecco or any other "monstor" fish should always go with much larger tank, even at the beginning. They get aggressive as they grow (I made that silly mistake of two pleccos in a 20 and overnight the one ate the other). It was just a quaranteen tank while waiting for home of 75!

The waste of plecco or any other fish (ie nutrients) as well fuels the algae - when the water chemistry is correct (ie plants, nutrition fish bio load) even with high light (see high light planted tanks) algae is hard to be able to thrive.

So, what I advice is to plan first around your situation.

If the light filtered? or a strong ray of sunlight (need to move the tank further from the window then) (not only that, but again temp swings, equals stress on fish equals disease) (cold/hot).

Choose a smaller school of fish for example, that will fit the size of the ten gallon, hint NO plecos or such larger fish. Many of the other algae eaters have their own problems (ie sensitive to water quality so on) so I will address water chemistry.

Algae is not harmful just for some it looks not nice. There are many types (some actually are) but you don't mention which?

Email me at sherryazure@yahoo.com and I will find a great link for algae types if you want.

First, get your aquarium plants. Do a search for what fits your size of tank, lighting and amount of time you wish to spend caring for them. Anubias are easy to care for if you can find them (online places ebay or aquabid makes it easy and inexpensive now).. they should not be planted (rhizome will rot) and can be on rocks, wood, floating or sitting on thin layer of gravel. You should not have more then 1/4 inch of gravel/sand (just enough for bio culture) if you do not have lots of rooted plants.

After this stage, let the tank mature naturally before adding fish. That allows the plants to start to grow and they will out compete the algae for nutrients!

Then slowly add your fish. A small school of cory catfish say 4-5 and a small school of say black neon tetras, white cloud mountain minnow (likes a bit cooler) or any of the other many smaller schooling fish (ten about in all, enough to not have aggression in the school, but keeps bio load down).

So, it is not just the light that causes algae, but nutrient control, waste control so on.

Even my huge round globe which is in the living room with right next to the only window this NYC apt has, and gets indirect lighting (reflected from hotel at back) never has algae! Please again, email and I can send links and photos.

Best Sherry