Maddybelle, I would've just saved those dishes in case I needed them again, no point in having to buy special dishes if you already have them!
With our guppies, my ACF's are the preferred culling method, but we have to do it within a certain size, or the frogs won't bother. When my needlenose gar broke his back, and when my pineapple betta had a horrible infection and couldn't breathe, I had to freeze, and I HATED it! I wasn't sure how long to leave them in, and I could only imagine how they felt, being so cold. :(