Fungus or Ick on Goldfish tail- PLEASE HELP!

Shippo is a long-tailed comet goldish with a serious tail issue. I lost my other calico goldfish to the same thing (R.I.P Mushu), I don't want to lose another. I have him in a 20Gal tank with a 50G filter, I also do a 50% water change every week. There are a plecco and two small new goldfish in the tank. They do not have any issues. For the last 2 weeks, I have been dosing the tank with API Pimafix for fungal infections and Melafix for bacterial off and on in 3-day intervals. The tank isn't temperature controlled at the moment and sits roughly at ~76F.
The treatment for ick I have read about involves salination of the tank to 0.5% concentration and taking the temperature up to 82F. I wanted to get extra opinions before I start adding more chemicals to the tank and taking up the temperature. Any ideas on what the heck is on my poor fish and how to get rid of it? This morning I noticed he has a new rip in his tail and some scales missing. I guessing his he is rubbing up on the decor that's in the tank.

Can you pot some picture that aren't moving and that show the whole fish and its fins?

Are any of the fish rubbing on objects?

What is the ammonia, nitrite, nitrate and pH of the tank water?

Have you added anything to the tank in the 2 weeks before this started?

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If a fish doesn't have a disease, you don't want to add any chemicals because the chemicals harm the fish as well as the disease organisms.

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Salt doesn't treat white spot and neither does raising the temperature to 82F.

You can kill white spot by raising the temperature to 30C (86F) for 2 weeks. It has to be that high or it won't do anything to the parasites except let them grow faster.

Other ways to treat white spot include Malachite Green or copper.
*NB* Malachite Green (aka Victoria Green) is carcinogenic (causes cancer) so care should be taken if you use this stuff, and avoid inhaling, ingesting or getting it on yourself.

pH: 7.4
Ammonia: <0.02 PPM
I added new fish ( the two small goldish) but they did not have any spots on them so I thought it was fine. Hindsight was probably a major mistake. Does this look like a case of ick?

Would the treatments kill my plecco and snail?