Cory behavior

I have 2 peppered corys in my 10 gallon along with 4 harlequin rasboras and 3 glowlight tetras. I did have 3 corys, but one died and I haven't added a replacement.

I think the corys are a male/female pair because one is much bigger than the other.

Will they be ok as a pair or should I add another cory to the bunch?

Also, the larger cory likes to swim up and down the walls of the aquarium, like she's trying to escape or something, and also swims through the bubbles at the back of the tank. The smaller cory does this too, but not as much.

I just did a water change, and all parameters are ok.

Is this normal playing behavior, or is something wrong? They are not going to the top of the tank more than usual, just swimming up and down a lot and are very active.

Yeah, TKOS, they're really goofy fish. I'm a little hesitant to add another cory right now as I'm waiting to see if everyone is ok.

The other cory died about 3 weeks ago, so I don't think there's anything else wrong, but better safe than sorry.

The 2 corys I have seem to be great little pals and hang out together a lot, so I don't know if it would be that great to add another one to the mix.

I am feeding them shrimp pellets at night after the lights are off, because the greedy tetras will eat them otherwise. The tetras are little pigs. I've been squashing the tiny snails in the tank and putting them in as food, and the tetras will grab one in their mouth and take off with it like it's a great prize or something.