Coincidence? "No Planaria" or bacterial infection

I have kept axies for some time, and I'm always reallt scrupulous with my tank cleaning, I syphon off any uneaten food after every feeding and use a gravel cleaner when I do my water changes.
I was really shocked a few weeks ago to inundated with little white worms stuck all over my aquarium glass- planaria. I've never had them in my axie tank, but kept a freshwater puffer several years ago, and had them in that tank- so I know they breed on excess food in the tank.
So I did some more cleaning....still loads of planaria.
I hate them, can't stand putting my hand in the tank knowing they are swimming around....mad really with all the live food I feed them, but anyway....
I read about treatments and that "No Planaria" had been used with Axies without a problem, so I bought some. I treated the tank with ha;f a dose, it looks like sprinkling flour on top of the water, very odd.... but the planaria went and I was happy.

UNTIL last week- roughly a week and a half post No Planaria treatment- my axies stopped eating and then one of them started floating, couldn't keep any depth in the water. So I fridged him for 5 days, and when I put him back he seemed fine, sank to the bottom and swimming about, for about one hour, then the floating started again.
So he's back in the fridge, and then another developed a lump on his side overnight and just lay on his side at the bottom of the tank, lifeless but breathing ....so he's now in the fridge too....and I have my fingers crossed he'll be ok but he looks awful...

All water perameters are fine, temperature is fine, nothing different.
The others seem fine. I've been doing frequent water changes a bit more generous than usual since the first axi started floating.... and today I've treated tank with methylene blue, half dose which I've used in the past without a problem....

So, I'm now thinking No Planaria wasn't good for them...but could it just be a coincidence.....?
I personally wouldn't risk using it again.