BN pleco illness, help please

[Ddt]

I had an angelfish and BN pleco living together, but my angelfish mysteriously died last week. I completed a water change and now it is just the BN pleco in the tank.
A couple of days after the water change, I noticed he had marking on his back which after doing some research I think is ammonia burns.
The days following that, he started developing white fluffy patches over his back and stomach, as well as white/light coloured stripes down his tail (I will try to attach photo).he was also not acting like his usual self, not moving much, seemed lethargic, although his appetite never changed. I treated him for fungus and the next day all of the white markings had disappeared and he was seeming more himself, however today now I have turned his light on and noticed that the white patches/stripes are returning on his tail.
Is this the fungus returning or is this normal for BN plecos to change their skin? I’m not sure how old he is as I adopted him off someone unable to care for him anymore just over a year ago.
Any advice is greatly appreciated!!

First photo is what he looked like before fungus treatment (unable to take photo of his stomach as not visible for long enough) and second photo is what he has looked like for the past year, with his usual pattern and colourings.

 

[Autumnsky]

Do water changes!!!! How long has the tank been set up?

Did you change your filter pads before all this happened?

Are you familiar with the nitrification cycle, it is the key to keeping a happy tank. There is an article link in my signature. It explains it.

It sound like this poor fella is having a pretty hard time. You need to get the water parameters to a safe level if you hope to get him better.

Test the water and see where you are at, and a liquid test kit is something which offers the better results.

**The local big box stores will price match their own online items or direct competitor, call and find out which ones they accept. Petco is also with Live aquaria online Petsmart is also with Chewy, so probably those at least, must be the exact same item.

Prime water conditioner and a couple others which take care of Chlorine and Chloramine - neutralizes Ammonia, NitrIte and Nitrate. To help keep your fish safer.

What are the levels for
Ammonia,
NitrIte
Nitrate

pH

TDS

GH/KH

Tank Temperature.

If you get it tested at the lfs, make sure to note what the numbers are for each item!!! They don't always tell you, but ask for that information up front.

If you do not have a test kit at least change the water right away.

Make sure to always dechlorinate the water. And get it very close to the same temp he is in presently.

Do several 30% pwc. One after the other, and then another to get the water cleaned up and make sure it is at a safe level.

These one after another water changes makes the changing water quality more gentle of a change to the fish.

Having the water not be toxic, is the best start for how you can help him get better.

He may start doing much better just having clean safe water.