I think I might try using a different type of dewormer next time as you said. I know two of the other boarders at the barn use Quest Gel a lot, but the other boarder uses Strongid. I've read up about dewormers a bit, but what do you prefer?
I did get to talk to my vet Saturday morning, and she mentioned taking Night off his grain and giving him only hay and water. This morning his feces already looked closer to normal. What I believe this whole problem is is he just has an imbalance in the organisms in his intestines.
The vet will be out tomorrow to take another feces sample incase she missed something. Hopefully nothing else will come up. Thanks for all the help!