Your not doing anything to help the fish over 4-5m in a freshwater dip, aside from stressing it out and possibly killing it. Glad that you never lost a fish, but this is dangerous advice. Successfully beating a disease doesn't mean taking already stressful treatments to the extreme, it largely depends on alleviating stress so the fishes system can recuperate.
OP - Stick to advice that has long been established as safe and sound. Links to freshwater dips and QT processes below:
Freshwater Dip (updated 7-30-2023) What It Treats: Provides temporary relief of some parasites - Marine Velvet Disease, Brooklynella hostilis, Uronema marinum seem most susceptible to the osmotic shock. A FW dip can also be used to dislodge certain crustaceans and worms, such as Parasitic...
humble.fish
How to Setup a Quarantine Tank (updated 4-6-2023) The following are the essentials: Aquarium (10-30 gallons seems to work for most people. A larger QT lets you house more fish and gives you more wiggle room when it comes to ammonia. A smaller QT is cheaper, easier to maintain and can be...
humble.fish