I would say you have some slime of sorts suffocating your roots.
As you can see from my posts I run live , so I would massage and wash that chit off.
And then use a bacteria to fight it.
Pouring my bacteria through my net pot.
Same would apply if you choose kill instead, I would then add my , bleach, pool shock, h202 into water and then apply as to not overdo .
Like mix your nutes and kill in your pail then switch pail.
Dip a Dixie cup in mixed up pail and pour a couple through the pot to help kill.
Were as I could dip my cup then add Hygroben in a much stronger solution pouring through my cup without harm.
Hope that’s not confusing.
Enjoy