[Sheldon31]

I think 10 might be a bit heavy on your bioload with a betta so I'd go with 8. Pygmy are smaller so I think you might get away with 10 but someone who has this specific type will be able to help more. I have the larger Bronze cory which grow to 3 inches.

I have play sand in my tank with my Bronze cories and they love it! It's actually quite lightweight and not sharp, a lot of people here have play sand with their cories. I've had no problems with plants being uprooted by my cories. I think cories will help reduce gas build up but I'd still stir it up once a fortnight to a month. (better safe than sorry)

 

[Sheldon31]

Unfortunately cories only really disturb the very top layer, so you still need to stir the sand, especially with the delicate little barbels on dwarf cories. I stir weekly.

This has answered my Q too lol was going to post something about this after it bugged me for a while.

 

[Sheldon31]

To be honest, Kyon only takes notice of my corys when I feed them their cat fish pellets. He will follow them, hiding behind plants like a spy until they find something nommy then he will nudge them out the way and snap the food up!