It would help as they would eat the algae, but then again, they breed and your friend may get overrun with goldfish. Depends on what he/she wants. I like goldfish, not everyone does.

You can also get a certain type of straw that is suppose to help prohibit algae.

I use pond salt in mine that seems to take care of the problem, but I have a small pond. I don't feed my goldfish, so between the salt and the fish eating the algae, I don't usually have much of a problem.

Min
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Min