help!!!!! Black Moor caught ICK

[Bitner24]

I have a blackmoor for the past 4 months and red cap oranda. my black moor was my first fish for about 2 months ago and I had a different red cap oranda which had ick and then wind up passing away. Thought it was ick than on her last day or two of lufe i thought it coykd hve been fin rot. Regardless i fixed the tank and the black moor "Bitner" never caught ick nd was fine for past 2 1\2 months. I got the red cap "Babs" probably 2 months ago, both are doing perfect until two days ago I bought a baby pleco about two and a half inches long. when I first got the common pleco my black moor was acting a little standoffish sitting in the corner the next day I left for 4 hours came home and saw my black moor had a chunk of its side missing not sure if the plecp had sucked on it or its fins scratched it, since plecos Fins are sharp. The lady at petland said pleco was fine to put in tank with goldfish. Just the fancy plecos with red eyes weren't. After Bitner had gotten hurt I read plecos shouldn't be with goldfish. as much as I didn't want to I called Petland and returned my pleco because I saw my black moor was under a lot of stress he also looked like he had a film on him as if slim coat was not there. immediately after I took the pleco out my black moor Bitner was swimming around perfectly, and red cap oranda "Babs" was no longer hiding under filter. After I bring my pleco to the pet store the manager told me it look like he had ick as along with the other fish that were in the tank. Meanwhile when I got the pleco she said he was healthy. I showed her the dots she said it wasn't ick. UNREAL -- she said to Just to put PRIMAFIX in tank the day I got the pleco. --- OneStopPlus cold out of my tank and she noticed he had told me to go home and dose my tank once with medicine just in case the fungus was swimming around. and then the following day change 25% and start up with the Prima fix once and double dose the slime coat to repair the damage side. Which I waited 2 days bc that is what medicine said to do, even though he did not have if I follow the instructions. Two days later which is this morning 8 a.m. I notice Bitner has ick on him

I treated with ick medicine 6 hours later i do 25 percent water change and add half a dose of prima fix since that is what manager at petland told me to do.& too much medicine could also stress out the fish.

Babs the red cap oranda is swimming fine all day along with Bitner the blackboar until 3 hours ago Bitner is just sitting at the top moving his fins just not swimming but still eating.

My fish that past from pick stopped eating so I'm looking at this was good news.

My question is, should I do another water change now?? My PH level is low how do I higher it? It at about a 6.4 when ideal is 7.2 --- even before Bitner got sick my PH level was never at 7.0-7.2