Brown stains have developed on the inside walls of my fish tank What are they

The way to tell the difference is that when scraping off cyano, it will come off in slimy sheets.

According to http://www.aquariumpros.com/articles/alg...

"There are many types of algae. There are also a few organisms that look like algae but are not algae at all. In a healthy aquarium, the algae will be green, and if left alone, will grow hair-like in appearance. Algae that is red or brown may indicate a water quality problem, such as high dissolved nitrate or phosphate levels in the water. Red and brown algae are also common in new tanks, when the aquarium is not yet ecologically balanced.

...

An aquarium may occasionally break out with an infestation of cyanobacteria, a slimy growth that grows more rapidly than algae. It may be green, blue, black or red in color. Unlike algae, cyanobacteria is extremely easy to remove but very difficult to control. Even if every bit is removed, it can quickly grow back in only a few days. Cyanobacteria thrives in well-lit aquariums that have excessive levels of phosphate in the water."

So it seems that both types of brown "algae" can be controlled by limiting the amount of nitrates and phosphates in the water.

One easy way to help control nitrates is to put competing species in your tank in the form of live plants.

This artice describes several kinds of easy plants that don't need special, high lighting.

http://www.petfish.net/kb/entry/247/...

If you use tap water, you could be getting high amounts of phosphates. There are various ways to battle this (some listed on that link). As my FW tank is small (6 gallons), I prefer to simply buy R/O water by the gallon.