Crusty Buildup

Question
hii! well we have this fish alk and it has a crust buildup on the tank and on the filter its kinda brownish and its like eating the pain off our walls its scary any idea what it is?

Answer
I would say that it is minerals from your water, mostly calcium, sodium, and magnesium, with some biological material mixed in. The easiest way to remove it from glass is by scraping it with a razor, on acrylic tanks you need a scraper and scrubber made for plastics. The easiest way to get rid of it is to prevent it. You probably have hard water in your area, which means it has more of the minerals than soft water. If you have hard water you probably have a high pH level in the tank as well. You can lower the pH with various chemicals available at the pet shop, just follow the directions and don't try to lower it too fast and wind up shocking and killing the fish. Another thing that can happen if you go too fast is that the chemical will actually cause the minerals to precipitate out making the problem even worse for a while. But once you get it adjusted the problem should lessen. Because of that precipitation it is actually better to treat the water separately in a plastic bucket or jugs and let it age a day or two, which you should do anyway when topping off the tank. When you pour it in leave a few inches of water in the bucket. There are also products you can put in the tank or better the filter box that are like bags of resins that are supposed to keep the water soft and the pH adjusted. You will want to get the pH adjusted with other means before using one, they are to 'maintain' pH, not adjust it and are not fast acting and don't last long if you try to use one to adjust the pH.
As far as it getting on your walls and eating the paint, lower your water level at least one to two inches to prevent the splashing out. I do not know how to get it off of the wall other than try some warm vinegar and or sand it off and to re-paint.
Hope this helps. Send a follow up if you have more questions.