Hi ilikefish,
So far as I know, significant growth of algea is a sign of an unhealthy tank. If you're not having troubles with the stuff I serously recommend you don't court it. Algea tablets are made of pure algae at the end of the day and your fish will do fine on them. If you want to supplement a Pleco's diet then there are other ways to do it:
Live foods such as Booldworms and Tubifex provide protein, as does a small piece of grilled chicken.
A slice of potato, cucumber or courgette (zucchinni in the US) are also good. Make sure to take the potato out of the tank as soon as it starts to turn black though. And don't leave the chicken in too long either.
Hope this is of help.
Scott