How much Algea can Goldfish tolerate?

The UV light in my filter burned out, but the Algea levels seemed to have
stabilized at a reasonable level. I have to clean the built in filter on the
pump about every three days. When the UV was operating last year, I could
see clear to the bottom of the pond. But so could the Heron. With the Algea
I have now it's harder to see the fish and they don't seem to mind.

So how much is too much.