Do Algae Eaters Really Eat Algae?

Hey mora. How is your test results?

I really hope you can increase the Otocinclus Catfish to at least 5. Once I ordered 6 of them, and they were really actively looking for algae everywhere in the tank. Two of them died much later one at a time. Once the number was down to 4, I stopped seeing them all together. They hid so well and I didn't see any of them for almost half a year until one time I moved a rock during cleaning. They just seem to get really nervous if they don't have the minimal required number in the same tank.