looks like a chiton to me. Push on it with your finger see if it has a hard shell.

I have a similar creature in my tank but its not flat at all looks more like a snail without a shell and mine moves alot?

stomatella snail

Wai's definitely has some. I bought a box there like a week ago. It's about half way in to the store on your right, on the very top shelf.

Wais is selling flatworms lol


Another option is a velvet nudi, but it only eats flatworms so a rental would be great.

Do you remember what price point they had it at?

+1

Doesn't look like a flatworm to me. My vote would be to just leave them alone. You'll probably do more damage to the rest of your inhabitants than good trying to nuke them, especially in such a small tank.