Thanks, Julia and 1beataway for your responses.

Julia-I've finally found a heater that I can order for the water! I've been looking for a while since winter is coming. I'm from a very small town that has nothing except one tiny private pet store with a tiny inventory. Anyway, I'm going to order the heater on-line. It's a TetraFauna Aquatic Reptile heater, 100W.
The wood I have in the tank came from a very clean lake here, and I boiled it for 15 minutes before using it. Same as the rocks and everything else in the tank. I can pick up a PH test kit and check it if it really could be a problem. The toads spend 95% of their time in the water.

1beataway- The toad hasn't eaten for almost 2 weeks. I'm not totally sure of his age, but he was in that classroom for 3 years, and prior to that they came from the pet store. I don't know how old they are when they show up in the stores, so he's at least 3+ years old.
Now, as far as the gravel, I know it's not great to use. In the 20 gal tank I had them in previously I tried soil, etc, and what a nasty mess. So I'm back to the gravel here, but there's mostly frog moss and the piece of bark on land, so I'm hoping he didn't ingest a piece of gravel. Now that the moss has proven to work ok, I'm going to cover the rest of the above water gravel with it. In this tank (except for the cricket I tossed in today) the toads have never 'free fed'; my son always hand feeds them, so I'm doubting he ate gravel. I'm really hoping not. What a horrible thought..........