Fish are not bothered by algae at all. Many of them even like to eat it.
If you do not like it , however, you can use an algae scrubbing brush and clean it off. It will also help if your tank is not in direct sunlight, which can stimulate algae growth. An algae eating fish often is not necessary.
It is great too see that your goldfish have lived for such a long time, but a bigger tank is really much better for goldfish. The bigger the tank, the longer your fish will live - and goldfish can sometimes live for more than 20 years!