Axolotl not eating after passing spermatophore

[GuitarFitz]

I have a male axolotl, that lives alone, that is about 8 years old and he hasn't been eating for over a week. Earlier this week on Tuesday I noticed that his rear end (I don't know the terminology and axolotl anatomy too well) had opened up and was very red and he passed what I believe was a spermatophore and he was swimming alot. When I disturbed the stones in the bottom of the tank I noticed many more blobs of sperm floating around but now his rear end looks normal again but he still doesn't seem right. I've also noticed that the end of his tail is curled, which I hear is a sign that he's stressed. He's still not eating, he keeps coming up and taking gulps of air and spends a lot of time floating near the surface of the water, motionless. This is the first time he's done this in the 8 years I've had him.

-Is it normal for him to go off food before, during and after passing spematophores?
-Is it normal for him to keep coming up for gulps of air
-Why has he begun doing this after 8 years, when there's no female around
-Should he return back to normal soon without me doing anything?

[Julia]

Here are a couple of questions

How big are your stones?
Do you test your water for ammonia, nitrate, nitrite.
What is the current temperature of your tanks?
Have you changed anything recently, like food?

[GuitarFitz]

The stones are around 7-12mm wide
No, I haven't tested the water for ammonia or anything. I have never done this and don't have the equipment to do so.
I have lost my thermometer but the water's around 20 degrees C. I'll buy a new thermometer soon.
I haven't changed his diet at all recently.

UPDATE: I noticed yesterday (Friday) a little white fluffy blob on his gill, which I thought was some of his sperm and when I tried to get it off he'd swim away so I left it. Today (Saturday, the white fluffy stuff had spread over his gills, looks like a fungus so I gave him a salt bath today.

How often and for how long should I give him salt baths?


Also, should I change all of his water? I changed about 30% of it today.