Black fungus or nutrient deficiency?

[Bluethunder98]

RH went up a lot for an hour one day next day I see black dots. I checked for critters and nothing was found. Should I cut off the leaf? The pictures show the progression of a few days it is only one fan leaf that is doing that (second to top node).
Temp 75
Ph6.0
Coco coir
GH nutrients

 

[mysticepipedon]

Opening Disclaimer: Let me start by saying I've never seen this on pot plants, so my answer could be totally worthless.

On ornamental plants I've grown, when there is a white fly or aphid infestation, the flies or aphids leave a sugary waste product that is eaten by a black fungus. The fungus doesn't hurt the plant, other than preventing light from hitting the leaf it's on, but it indicates a problem with white flies or aphids.

Closing Disclaimer: This message is a slightly informed shot in the dark.

 

[Bluethunder98]

Opening Disclaimer: Let me start by saying I've never seen this on pot plants, so my answer could be totally worthless.

On ornamental plants I've grown, when there is a white fly or aphid infestation, the flies or aphids leave a sugary waste product that is eaten by a black fungus. The fungus doesn't hurt the plant, other than preventing light from hitting the leaf it's on, but it indicates a problem with white flies or aphids.

Closing Disclaimer: This message is a slightly informed shot in the dark.

Thanks I appreciate it!