:iagree: No fish will eat the hard spot algae, it needs to be scraped off manually. If bristlenose plecos and otos could rasp hard enough to get the green spot algae, they'd shred your plants....which does not happen. They really don't rasp like some other plecos, they suck.The hard spot algae is too difficult for many "algae eating" fish including otos. They may be able to eat the newest growth but a scrubber, scraper or even a razor blade is needed for the stuck tight kind. If you can't easily rub the algae off with your finger, chances are the otos can't eat it.