My friends got me a betta for me after I took a gruesome standardized exam to replace my old fish (long story short, he jumped out of his tank during one of the very few instances when I left the lid off). This was only five days ago.
This new fish Tiberius seemed to be fairly active when I first got him, and he seemed to be just his cheery old self last night when I went to bed. However, when I woke up this morning, I found a large patch of pale grey/white on his back and near his tail. It is not fluffy or fuzzy. His top fin seems to have clamped together and he barely moves. He also chooses to stay only at the surface.
Now here's my set up:
He is housed in a five-gallon tank (friends got this for me with the fish) by himself. It has a filter but no heater. I have been monitoring the temperature, however, and it has always been steady around 80 degrees. Since he seemed like he barely had the energy to move, I turned off the filter so avoid further turbulence in the water that may exhaust him more; I hope that was the right thing to do.
Since like I said there's a filter, and I've only just gotten him, I haven't had the chance to do any water changes yet. I had planned on doing that tomorrow actually.
I usually feed him Hikari's betta pellets (about 3-4/day), which both Tiberius and my previous fish seemed to enjoy. I have also fed him a freeze-dried bloodworm once since I've gotten him as a treat. He seemed to like it fine.
I suspect that Tiberius has some sort of fungal infection from my very superficial knowledge of betta diseases (my previous fish was completely healthy for the 11 months I've kept him), but there's no fuzz growing from his white/grey patch. I tried to take a picture, but it doesn't quite show, and I would rather not stress him further.
What is wrong with him? What should I do? Any help would be appreciated. Thanks.