Algae is harmless to your fish. The only dangerous 'algae' is blue-green algae which is actualy cyanobacteria (sp?) and releases toxins into the water.
Brown algae can be caused by a number of things. Firstly, it is natural for a new tank to go through a phase where it has lots of brown algae. This will normal clear up or be replaced by green algae. If this doesn't happen, it means you have insufficient lighting in your tank.
The best way to reduce ANY algae though, is to decrease feeding and increase water changes. You are probably over-stocked or over-feeding at present - silver dollars are very big, messy fish. These are the kind of things you need to phocus on to permanently get rid of algae. Increasing the light would also encourage green algae to take the brown algae's place if this is something you would preffer. Adding plants - especialy fast-growing species - would help to use up the minerals the algae uses and compete with it. Eventualy, if you keep scraping algae off, the plants would take over. However, I can see how planting the tank could be a problem with silver dollars
To temporarily get rid of algae, scrape it off from the glass but leave the rest of the tank alone. By leaving the remaining algae, besides giving a more natural appearance, you are making it more difficult for algae to re-grow on the glass where it hinders viewing the tank.
Another option is to buy an algae-eating fish. With silver dollars, a pleco would be ideal.
