Read this post it will give you some good information:
They are diatoms. How are you lighting the tank? They are normal, and found in almost every tank, but can be especially bad in newly setup tanks.
It won't hurt your cycle to clean it off your decor/glass. You can use a toothbrush or something like that to remove it.
Here are some step you can take to prevent them:
You really cannot entirely "stop" the growth of any algae, green brown, or red, but with some good tank management practices, the rate of algae growth can be reduced. There is no such thing as an algae-free aquarium. An aquarium that never gets any algae growth is probably not a healthy environment for fish. Algae should never be controlled through the use of chemicals. Most algae-control chemicals work by inhibiting the reproduction of algae, and may also inhibit the growth of plants and beneficial bacteria. We have seen some disasterous results caused by over-use of algacides. These chemicals should only be used to get rid of green water or very bad algae problems, then good tank management alone should be used to prevent re-occurrences. It is important to remember that algae is a "plant-like" organism. Unlike a plant, it has no true roots, stems or leaves. Like a plant, it needs plenty of light and nutrients to grow (it already has the water). The first thing to look at is light. Aquariums should never be placed where they can receive a lot of direct or even indirect sunlight. Tank lights should be on no more than ten hours. The next factor is nutrients, and in aquariums, this means controlling nitrates and phosphates. Regular water changes and good filtration are important to eliminate nutrients. Vacuuming the gravel in a tank when doing a water change, removes many organics that decay into basic nitrates and phophates. A 25% water change every three to four weeks, or 10% a week, will help control the build-up of nutrients. As most city tap water contains phosphates, using reverse osmosis, distilled, or deionized water will also help. Using phosphate and/or nitrate removal media in a canister or power filter is also helpful. Water motion will also inhibit algae growth, as algae spores cannot settle and take "root" in an aquarium that has good circulation. Using small submersible pumps or powerheads in a tank, in addition to the regular filters will help add extra circulation to any aquarium.
Hope this helps.