At the moment while he is unwell try to keep the water spotless, in a 5 gallon if it's at all possible do a 80% water change every two days if the tank is not cycled. Preferably condition the new water and bring it up to a matching temperature before changing the water. If you can buy or borrow a heater do so; keeping him at a steady temperature will help reduce any stress and improve his chances of surviving.
You could look at reducing the tank volume by half so he doesn't need to swim so far to breathe (in this case do a daily water change).
If it looks like he has velvet treat him for it; just remember to remedicate each time you do a water change.
Water temp is going to be a few degrees lower than room temp so right now he is pretty cold in the tank you have him in right now. He needs to be in water with temps of at least 78F and that are kept stable. This needs to be measured with an internal thermometer as sometimes the thermostats on the heaters are not as accurate for various reasons. So if you set your heater to say 78F it actually could be more like 76F or so in the tank which is why a thermometer is recommended to make sure the water itself is as warm as you need it.
As for water changes, on an unfiltered tank, I recommend 100% water changes every 2 days and try to match the temperature as closely as possible every time.
Thank you for your advice!
I have bought a small heater today and put one of my thermometers in the tank to monitor the temp.
The Betta is looking better and better everyday, his bottom fin is starting to spread out as usual and his top fin as well, the other ones are not so clamped anymore. I'm confident about bringing this little guy back in line
He's still not eating tho but we'll see tomorrow how he feels about it.
Still didn't eat anything today but he looks better and better. His tank temperature is the same as he was in the other and I'm sure he's happy about it!
I'm staying home today so hopefully I can monitor all of this.
It seems that he likes to eat the pellets after all!
He is towards full recovery!
I'm wondering how long should he be in the quarantine tank for?
He still is showing a bit of clamped fins but only on one of them and its the end of the fin that is not spreading 100%.
Little update on this, I might have been excited a bit too early, I still see his top and one half of his tail fin a bit clamped.. I don't see much progress on this. He is also not making any bubble nests anymore.
Have you done anything differently between the times that he was looking better and now? Maybe you stopped doing something because you thought he was better? Just keep at it with water changes, making sure he eats etc like you did before and hope he goes right back to feeling better. Good luck!
Keep up with your water changes, keep him warm, and make sure he is eating and acting good for a while before you add him back to the main tank. I wouldn't worry too much about the bubblenests. They really don't mean much besides the fact that he is old enough to spawn.
Well I haven't done anything different no!
I'm doing 95% water changes every other day, remedicate at the same time (a bit of aquarium salt, a bit of med + prime) and make sure the water is the same temperature than his tank.
He eats every day, pellets of various sorts, and I gave him a frozen bloodworm as well.
A good update now, his top tail fin is about to be not clamped anymore
I guess I might have been scared too soon.
Good thing I don't have children, I'd rip my hair off at the first sign of disease!