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You wrote-"All levels of water are tested and fine" .
What did you test for and what were the exact results?
Also, how many gallons of water does the tank hold?
Thank you for the information.
Before I begin I'd like to touch upon water quality and water testing.
Proper test results should always indicate:
Nitrates= 20 ppm or lower
The 3 results you supplied, ammonia, nitrates and ph were all fine but there was no test result for nitrites. Nitrites are an important factor and if they are indeed present, in any amount, they will cause serious problems and fish deaths so I urge you to test for them too as soon as possible as my recommneded treatment plan will not work if lethal nitrites are indeed present in the water.
The symptoms you describe are an indication of parasites (red string like things coming out of fish's gills) and a fungus (white fuzzy things on smaller fishes mouth).
At least one of the medications you administered should have cured the fungus problem so I suspect there might be a potential water quality problem or maybe the fish just needed to be treated for a longer period of time.
What I recommend be done is:
1) Cease using all the medications you've been using up till now and begin to treat for parasites with a medicine called Clout, click on 1st link below for a view of the product which can be obtained at pet stores and online. Follow the directions on the product label for usage/dosage instructions.
2) After treating with Clout begin to treat with a medicine called Fungus Cure, click on 2nd link below for a view of the product which can also be obtained at pet stores and online.
Note: As you've done a 100% water change the tank has effectively become a "new" tank and thus will begin to go through the cycling process. If you're unfamiliar with the principles of cycling I have enclosed a link below, the 3rd one, which will supply an overview of the subject which if I may stress is extremely important to know about and handle.
I'd also suggest testing the water every 3-4 days for the items mentioned earlier.
Remeber if ammonia and/or nitrites are present in any amount my treatment plan will not work. You might need to seperate the fish into a quarantine tank and do frequent water changes.
Best wishes and let me know if you have any questions.