Thanks for the responses!
Regarding the water heater thing- I've never used one, nor do I know anyone who uses one. The problem here is their water tank is metal, I should've changed it out with a plastic one as soon as it started getting cold and I feel stupid for not doing it, so that's all my fault.
I had to work until seven yesterdy... I would've taken off, but the other girl I work with was sick, so I couldn't :/ Made me a nervous wreck all day! Luckily my dad could atleast check on him.
When I came home I mixed up his normal grain ration, but added some mineral oil and prune juice. (Anything to get everything moving) He started out a bit more interested in his food, but only ate about 1/4 of it and then I had to encourage him to eat another 1/4. I moved my three year old out of the field with him so that I could moniter how much water/hay he was taking in. I also changed out the water tank with a plastic one, which didn't freeze at all through the night. I gave him some hay different from his roundbale aswell. Set my alarm for 1:00 AM to check on him.
At 1:00 I mixed up some apples with some mineral oil, prune juice, and electrolytes. He wasn't interested whatsoever. He had ate all the hay I gave him, but hadn't drank any water. (If he had, it wasn't enough to make it noticeable) I walked him a lap around our feild to get help everything move. I put some maple syrup (no molasses on hand... I thought I had some, but couldn't find it) in his water to make it sweet to encourage him to drink. I got probably about half a bottle of mineral oil in him (I had like 3/4, but some dropped out of his mouth). Gave him more hay, and set my alarm to check on him early in the morning.
This morning he had drank some water, not a lot, but some. (which is better than none!) He had eaten all his hay, the majority of the apples, and the bit of grain leftover from lastnight. I gave him a bit of grain, not a lot, with mineral oil and prune juice. Gave him more hay as well. Still not as eager as normal, but he's definitely looking better. Going to check on him in a little bit and I'll probably try and get some more mineral oil in him aswell.
Also- I listed to his belly several times throughout the night. At 7:00 and 1:00 there were no noises, but this morning he was a little gurgly. Which is normal for him, he's a very gurgly and, uh, "gassy" horse all the time, so I'm taking that as a good sign!