When you say his scales are sticking out, does he look like the photo below? This indicates a serious condition called "pineconing" and dropsy.
I would STOP the aquarium salt. It contains sodium, which puts stress on the kidneys, and can cause fluid retention and bloating.
I would try using Epsom salt. It has fluid reducing effects, so it may help with the buoyancy issues and fluid retention. However, it won't treat the underlying condition that's causing the pineconing/dropsy. And, unfortunately, by the time they start to pinecone, the internal organs are struggling to function properly.
Here's one way to add Epsom salt to his tank:
- Add 3 teaspoons Epsom salt to one gal of conditioned water.
- Stir/shake until the Epsom salt is completely dissolved.
- Using this premixed treatment water, make 25% water changes every 15 min for 1 hour today.
(This will bring the dosage to 1 tsp/gal.)
- Tomorrow, put a small amount of tank water into a cup.
Stir in 3 teaspoons Epsom salt. Make sure the salt is completely dissolved!
Over the course of an hour (or more), slowly pour the solution into the tank.
(This will bring the dosage to 2 tsp/gal.)
- Every other day, do a 50% water change every day, using this premixed treatment water.
(This can be done for 14 days, if needed.)
Epsom salt is inexpensive, and you can get it at supermarkets and grocery stores. Look for 100% magnesium sulfate. (No dyes, perfumes or additives.) Since it doesn't contain sodium, it won't stress his kidneys (like aquarium salt does). Look for 100% magnesium sulfate. (No dyes, additives or perfumes.)
Also, feed small meals of high-quality high-protein foods. The mosquito larvae that you have are EXCELLENT! This is what they eat in nature, so you're giving him good nutition that's easily digestible. If he doesn't eat, simply remove the food and try again later.
You can also cover the top of the tank with plastic vegetable wrap (Saran wrap). This will increase humidity levels, and make it easier to breathe. Be sure to leave several inches of air between the water and wrap, so your fish can breathe!
Putting the tank in a dim/darkened and quiet location may also help calm him.