Im not sure if hes sick or not?

Question
I have an adult guppy. Have had him for about 6 months. I bought 2 guppies originally and one died 2 weeks later and "wallet" ( our 3 year old named him) looked distressed after his friend died... He had a bout of fin rot which I treated and was fine, though his tail fin is not the same shape anymore, it's still frayed it's mending but not completely yet. That was about two months ago. since getting him six months ago, I have researched immensely about them. Problem: my mother in law gave me two 2-3 month old fry, and they are doing great, doubled in size first week! But my older male is acting sluggish and almost as if he's struggling to swim( like his tail was really heavy)... Sometimes has labored breathing(fast) and occasionally he'll get bursts of energy and dash to the bottom. Other times he'll stay on the bottom. Yesterday he had what I thought was clear poop, but today it's normal color but looks encased in the clear stuff like a sausage. His gills are open farther then I feel a normal guppies should be and they look like he's shedding or almost a haze around his gills. I thought he may have overeaten, because sometimes he's active and other times he's not. He has shown no interest in mating with the other females, although they are far smaller than he is... I'm putting salt in about 1tsp with aquastart and I'm doing that with 30-40% water changes daily. I'm trying not to use meds, but I do have quick cure for ick and protozoan parasites... Should I go ahead and give that to him?? Also, another thing I am thinking is I know I need to get them in a larger tank... The babies are small now, but it will stunt growth, as well as stress my friends, they are in a 1.5 gal tank. I am getting a 10 gal on Friday... I am going to try and cycle it before I move them as to not cause them MORE stress then I already have. Does he sound unhappy/sick/both because of one another? Any suggestions? And I know I'm not the perfect pet owner, but I am trying to be, by educating myself now, though I should have before I got them. I just have really become fascinated by them and would love to see them happy and healthy!

Answer
Okay, this is an immediate issue.  This has to be fixed today, no later.

He's showing signs of ammonia/nitrite poisoning.  Filtration isn't compensating for the new fish and the water needs changed asap.

25% to 50% today.  No way around it.  It has to be changed, or you could lose him.

Do not give him any chemicals.  He's not sick from an infection.

The shedding is because ammonia is burning his skin.

This is very common in aquarists.  

You need 1.5 gallons of aquarium per one inch of fish, but you have 3, and they will be at least 2" to 3".  You need at least 10 gallons to compensate for them.

I would stress the tank increase immediately.  Today.  

Filtration needs to be a larger filter than for a 10 gallon.  Get one rated to a 20 and you will have many less issues in the long run and it's well worth the extra $5 you have to spend on a bigger filter. :)

Happy fish-keeping...write all you need.  I will be here off and on.