Sadly, keeping it with fish and at those temps was a big mistake :S
These guys need COLD. Anything above 22ºC is potentially dangerous, specially for animals that are not perfectly healthy.
The ideal temp is below 20ºC. So, i´d try to lower the tmep in his tank a bit, since it will feel much better and it will boost it´s inmune system. IF the infected area shows no signs of recovery or continues to grow, you may need to give the newt salt baths (you can find info on that around the forum), or maybe fridge it. Hopefully you won´t need to resort to that.
Bloodworms are fine but can never be an staple, because they are not nutritionally complete. Get some earthworms. they are the ideal caudate food. They are nutritious, rich in calcium, and all caudates find them irrisistable. Since variety is always best, you can suplement it´s diet with waxworms, small crickets, blackworms, small slugs, isopods....
They are indeed very aquatic and in ideal conditions they will very rarely go on land (if ever), so you can consider it 100% aquatic. It´s a rather inactive species. They like to hide and stalk for prey, so don´t be surprised if it moves little.
It´s a bit late now, but you might want to consider changing the substrate. Gravel fo that size can be ingested causing impaction and even death. also, it traps dirt and uneaten food in huge amounts which then compromises your water quality. Fine sand is a far better option for a substrate.
Since in order to recover your newt needs as perfect conditions as posible, i would encourage you to add hides if there aren´t any already. They are territorial (and agressive towards other newts, even their own species) so they very much like to have their own hides to feel secure. That will contribute in reducing stress and giving a break to it´s inmune system.
PS: sadly there is no caresheet for any Paramesotriton on CC but you can find a wealth of information around the forum, specially in the section dedicated to Paramesotriton and close relatives.
