Fill out you're Cory shoal first, especially if they are all the same type. Cory's prefer groups of 6 or more, although they will not eat much algae. If there's stocking room left in the tank a group of Oto's are really good at algae removal.
Agreed. Corys love to feel comfortable with a decent shoal of at least 6. They will explore more, and be less startled when walking around/making noise, etc.
They DO NOT eat algae. I believe they eat a bit of detritus. They are a decent clean up crew but be sure to feed them their own food regularly, scraps are not enough and are often not available to them until the extra food is rotting away(like flake food.)
Ottos would be a good idea but expect to lose some a few weeks after purchase. They have a much smaller bio load compared to say BN plecos.(even with two plecos, 6 ottos may even have a smaller bioload than the two plecos., MAYBE, but you get my point.) They also need to be kept with at least 6 others, just like corys. Corys and ottos are also VERY compatible species. When I started out, I had 3 ottos and 3 corys, and both species kept together for extra comfort and safety.
Keep in mind, algae eaters are not a good solution for algae control. They tend to only eat specific kinds. Snails are probably the best. I would also note Siamese algae eaters would probably be the best preventative measure, especially if you have snails to eat the slime. SAE I believe eat filamentous algae which is the real PITA. They probably won't go well with your stock though. Sorry if I sound like a broken record, just throwing this stuff out there.
