White fuzz growing on guppies

[Shotaling]

So I've had this a couple of times before and thought I had it figured out. I occasionally get some guppies with this white cloudy looking fuzz on their bodies. Previously I've treated with salt and had around 50% survival rate after treatment. Looking to find out what this disease is and why I'm seeing it so I can better treat it in the future. Thank you for any help!

Water Parameters:

pH: 7.6

Nitrates: 5ppm

Nitrites: 0ppm

GH: ~15 degrees

KH: ~10-12 degrees

Ammonia: 0ppm

Water temp: 78-80F (past 2 weeks to assist with salt treatment, normally 72-25F)

[Levi_Aquatics]

@Colu is probably going to be able to help you the best

[Colu]

It could be the start of columnaris with the white patches that would explain the high mortality rate or an opportunistic fungal infection if only one fish is showing symptoms I would quarantine and treat with kanaplex and Jungle fungus clear fizz tab's containing nitrofurazone following this treatment plan if more than one fish has it than I would treat the main tank @Shotaling