paph rothschildianum leaf issues

[Setter]

What are the yellow spots on my paph rothschildianum?
This orchid is growing in a grow room, temp 75-80, humidity 65%, medium light, good air circulation, kept evenly moist with RO water, fert weekly / weakly, potting medium small bark with perlite and charcoal added. Thanks for your help!

[SouthPark]

How long roughly have you grown this plant for?

If it's been growing for a relatively long time, and the fertiliser application is every week, could maybe consider possibilities of fertiliser salts accumulated in the media ----- and too much fertiliser. So perhaps a repot with new media, and check the roots while at it.

Also check to see if there's any mites or something ....... very small, and/or scale insects. Not sure if you get mites or scale insects over there. You might not - as your plant is in a grow room.

[Setter]

I've had this plant since December of last year. It was repotted the middle of March, 2019. Growing in a clear pot so roots look good. Fert only while actively growing. No mites or scale.

[SouthPark]

If this were to occur in one my paphs, I think I would just spray my whole plant with a bit of mancozeb to start with, followed later by yates anti-rot, and then watch it like a hawk for the next couple of days. And if I notice significant spread during any of this time --- I'd likely cut off the leaf (using all the general sanitary procedures for orchids).

This is probably unrelated ----- does your plant sometimes get calcium/magnesium treatment? I usually rotate my relatively weak fertiliser and weak cal/mag treatments. Alternating..... like 1 once every three weeks, I give weak fertiliser solution. Then a few weeks later, weak cal-mag solution. The rest of the time in between is just regular tap water.

[Setter]

I give a low dose of Cal Meg once every 3 to 4 weeks. Once or twice a month flush with RO water. I'll try the mancozeb. Thank you.

[SouthPark]

Originally Posted by Setter

I give a low dose of Cal Meg once every 3 to 4 weeks. Once or twice a month flush with RO water. I'll try the mancozeb. Thank you.

Thanks for letting me know. All the best. The plant doesn't appear to be in any great danger from the looks of it, as you've been keeping a close eye on the plant. A very nice plant indeed.