First, I am very sorry you lost your Oscar. That's a bummer. They're wonderful fish.
Picking apart some of what you offered for clues.... Why did you cycle the tank with an Oscar in it?
Thank you, and the reason I cycled my tank with an Oscar in it was that I wasn't aware of the whole culture system in a tank. so when I found out that my tank needed to be cycled, I did daily water changes and water tests every 3 days until my tank was cycled.
Do you know why your other Oscars died? That's a red flag right there that something is probably wrong in the tank.
I have stated this in the very beginning. I don't know why my oscar died. that's why I made this post.
African dwarf frogs only get about an inch long so everything in there would eventually eat them. These are the little bitty guys, right? Not African clawed frogs (totally different species and problematic for entirely different reasons).
again, this was discussed before, but thank you for your advice. I do understand that the frogs won't grow big and will be eaten if left with the fish as they grow bigger.