They'll be eaten in days (they're not all that giant, even the most giant ones) and it's possible they'll kill your Bichirs with their spines in the process. With enough plants you shouldn't have much algae. Nerite snails might be your friend if the fish won't eat those. I don't have algae eaters in most of my tanks and I only have to scrape algae off the glass every few months. The only tank with algae problems gets more direct sunlight than others and actually has algae eaters (amano shrimp, nerites, snails) but none of them keep it under control. I've recently added pothos clippings in hopes that these help.