Beginner: Clean a Bowl
If you choose to use a goldfish bowl over an aquarium tank or outdoor pond, you will have to change the water almost daily because all goldfish in general produce a lot of waste and ammonia (see more about this topic at Nitrogen Cycle). By adding a layer of small gravel and a few living plants will help keep the water clean longer. If you decide to add an algae eater, you will need to give him space too and you will need to keep the water around 77F/25C. This might require you to buy a heater if your water temperature is to cold (see why this is not recommended at Goldfish and Algae Eaters).
To clean the water take out 50% of the goldfish bowl’s water and replace it with clean water none chlorinated water. If you are careful and don’t take a long time to do the water change, you can probably leave the goldfish in the goldfish bowl you are cleaning (see more about why at Goldfish Diseases and Goldfish Water). During this time you can scrub off any algae with a clean rag with no chemicals or detergents in it. We recommend an algae scrubber that you can get from your local pet store. But remember, a little bit of algae is a good thing (see more about this topic at Goldfish Food).