Ugh! Malfnunctioning heater on Betta tank!

Dang heater on my old bettas tank just decided to go out of whack. It's a 2.5 gallon heater. The betta is something like 3 years old, maybe more. I really can't remember.

This is the one that had a fungal infection about a month ago, brought in by live plants I stupidly did not quarantine. I had treated him with the fizzing tabs and he recovered quickly and has seemed just fine.

Just an hour ago or so, I came home from work and found him on his side at the surface of the water. He's alive and would occasionally swim around. I felt the water and it felt WAY too warm. Went to check the temp on the thermometer and it was not working right -- looked like a thermometer I had in the camper once that got too hot. Top temp on this thermometer is 110 -- hoping it didn't get that hot in there! I pulled a thermometer from another tank and checked -- 83 degrees. No new fish have come home in the last two weeks at least, so hopefully no cross disease contamination on nets or anything.

I grabbed my bucket and put water (and aquaclear) in that was just one degree cooler and moved him over to that. Every 15-20 minutes I lowered by a degree. He's now at 76-77 degrees. I hated to drop it so fast BUT he looked like he was on his last leg (Fin?)

He's now in my water change bucket (will sanitize later) on top of the 55 so it doesn't get too cold. The light hood should help that and it's 72.5 degrees in this room.

Anything more I can do for him to give him a chance? He's kind of laying over on his side some but can swim normally for short periods if something moves near him but then goes back to his floating.

To Summarize:
3+ years old, 2.5 gallon tank, found the overheating tank at 83 with a malfunctining thermometer (both of which were fine this morning -- was reading at 78 at 7 a.m) Fish had a fungal infection a few weeks ago. I haven't checked ammonia etc yet BUT he gets a 50% water change on Thursday and Saturday every week so had just had one yesterday.

Any ideas?

What I'm suspecting is that the heater had stuck on and gone WAY higher while I was gone then come back down to 83 by the time I came home. The thermometer had done something funky and won't even register a temp anymore.

I have him in a bucket for the moment, on top of the 55 (on the light hood) to keep him at a decent temp. He's sitting at about 77 now and is swimming upright a little more often, maybe.

It could be age, it just is odd that the temp that has been a steady 76 was suddenly up to 83 and the thermometer messed up all at once (as if it had topped out on it's high temp). We'll see how he does...will keep everyone posted.

I'm crossing my fingers about this guy. I had to leave for a few hours and he was still bad off when I left. I gave my husband instructions to check the temp in his bucket of water every half hour while I was gone (I'm sure he checked once all evening, but that's better than nothing!). He said when he check him he was on his side but alive. When I got home a half hour ago he was in a normal position, looking close t normal though not swimming madly or anything. He is still looking about the same now, so greatly improved from when I left.

For now, he's in a bucket with a few inches of water (so he can get to the top easily if he wants, with little to no effort) set on top of the 55 gallon. I figure that so long as I don't turn the heater down in the house like normal the residual heat will keep him at a comfortable temp (so far, it's staying at 76 or 77 up there).

I am convinced that the heater overheated tremendously while I was at work today and was cooling off by the time I got home. Crossing my fingers that Blue will still be with us tomorrow. (And tomorrow, I break down his little 2.5, sanitize everything thoroughly, give him new gravel, toss the old gravel in the flowerbed or out by the pond in case anything leaked from any tiny undetectable holes in the thermometer, and then reset the tank up so he doesn't have to live in a bucket. I guess I'll also have to run to town for a heater for his tank since I'm sure not putting THAT one in again!

Amazingly, he is not only still alive but he is swimming normally AND was begging for breakfast this morning. I fed him 3 pieces of his Hikari betta Bio-gold and he gobbled them up and looked for more (though he didn't get more).

I still have him (temporarily) in a bucket on the light hood (For some warmth) about 4 feet from an overhead heater vent. It's maintaining his water in the 76-77 degree range so I'm not too worried about that. (However, I'm switching him to an ice cream bucket later because he's in the bucket I use while doing water changes on small tanks and I'll need to sanitize it so I can use it today.)

Later today I'm going to break down his little tank & sanitize it thoroughly and set it back up...and go get another heater for it (though not the Hydor brand, will get another Jr. Aquatics--they are the only 2 brands of small heaters available here.)

Well, in case anyone is interested I figured I'd update...

Blue is swimming and acting 100% normal now. He ate well today and would have liked more. I switched him from a water change bucket to an ice cream bucket (not big enough for long term but he'll be back in his 2.5 in a couple days) which is still sitting on the light hood since it's keeping a perfect temp for him. The other fish will just have to swim to the other end for one more night to get away from the light.

I increased the depth of his water by about 3" from what I had him in to recover and that has created no problems. He's not back to blowing bubbles yet though I saw evidence of a few in there.

I think he's on the road to normalcy.