yellowish/tan splotches on Oncidium leaves

[Sahlabiya]

I'd love advice for the orchid I've had the longest (1 year 3 months). It had been through some root rot which I caught 2 weeks ago - the new growth was white and turning into brown and black. I pulled out the infected 'hearts' as I was advised, and dusted w/ sulfur powder. I clipped all mushy roots I could find, and let it sit and dry for a day. Then I brought it to the nursery where I bought it - they helped me to make sure there weren't any more rotten roots, soaked it in Banrot, prepared a special mix of media that includes fine bark, shredded New Zealand Sphagnum, small pumice, and small alifor.

After this treatment the leaves look the deepest green I have ever seen them...except for these weird brownish-tan blotches that keep occurring. I cut a couple of them off earlier, thinking maybe they were due to shock, but more and more keep happening. I haven't seen any new growth that looks good. I have found some more small black/brown small leaves/hearts - but they could have been in process before.

I am attaching photos. Since the root rot, I have been watering only once a week (from March until I noticed the root rot I was watering twice weekly) I use 20-20-20 fertilizer each time I water. First I let water run through the plant, then I water with the fertilizer mixture. I've been doing this since I got the plant. I move it around a bit to keep it in bright, indirect sunlight. It's possible that it gets some sunlight that is more direct than indirect - I'm not completely sure about the dividing line. Earlier in the spring I was putting it out in the mornings in dappled shade and this helped multiple spikes to grow and it flowered beautifully.

It seemed to get sick about the time I started keeping it inside to avoid 100+ heat and using my swamp cooler. I live in Tucson and it is usually dry but Monsoon Season is starting and humidity has really kicked up as well.

I would be so grateful for help with this - it seems like it is probably a fungus of some type?

[WhiteRabbit]

The dark spots may be from the dampness. Oncidiums are often prone to this kind of spotting. Fortunately, it usually doesn't harm the plant. Using a fan may help prevent, or decrease spotting.

The other areas might be burn, but I'm not certain (looking at this on my phone, so not able to see them well, sorry).

Hopefully others will chime in.

[Sahlabiya]

Thanks,

I'm attaching two more photos that are clearer - they show the parts that I originally cut off (there have been no more like the brown tip - I suspected it might be salt toxicity so I flushed it well with distilled water at the time).

Yesterday I cut off all of the parts that looked brownish tan and sprayed the whole plant with fungicide. The dark spots seem to be going deeper into the plant on several leaves now and I noticed that the tips of two aerial roots are tannish-brown. I'm wondering if there is left over fungus from before, and hoping that if so, I can get rid of it...

[WhiteRabbit]

The leaf in the last pic may just be dieing naturally. Is that bract foliage?

[Sahlabiya]

I'm not sure how to tell on an oncidium which is bract foliage - but I feel happy now that more than a week passed since I cut that off and no new brown tips have shown up. I'm being more careful about the light I keep it in too. In earlier summer it seemed fine in my West window in the afternoon, but now maybe that was causing burn. So far no new brown splotches.

I'm wondering if I should cut back the leaves with the darkest black dots? They begin to look like several of the photos I've seen of brown rot but not really sure how to tell.