There are many things that can go wrong, but these frogs are pretty healthy. Metabolic bone disease is something that can happen easily if they're not provided enough calcium. I encourage you to download the book "African Bullfrogs" from amazon and read the diseases and disorders section. The biggest thing to remember is that if your frog gets sick, by the time you notice it it will almost always be too late, so don't kick yourself if your frog dies. Also, my opinion is that bringing a frog to the vet is a complete waste of money.