Oncidium Leaf Tip Burn
 

:hello My Oncidium Tsiku Marguerite has been doing well currently with multiple spikes. Noticed dead leaf tips and an increased number of black spots. Wonder if this is classic in appearance for a diagnosis or within normal limits.

Location: Midwest
Medium: RepotMe bark topped with sphagnum
Light and climate: North-facing windowsill all spring and summer into fall. Moved under lights a week ago - RH average 57%. 24Watt LED receiving ~100 PPFD.
Water: 1-2/week. Tap water (PH 7.3, Ca 30mg/L, ?Mag)
Fertilizer: Miracle Grow Orchid 30-10-10 about every other watering. 1/8 teaspoon into a 1/2 gallon watering can

Considerations:
1. Salt build-up resulting in fertilizer toxicity.
2. Dry climate, possible dehydration (I shriveled the pseudobulbs in late summer a few times)
3. Nutrient deficiency
4. Sunburn (probably unlikely)

Would appreciate any thoughts!

Oncidium Orchid - Album on Imgur

Temperatures? My experience has been this one doesn't like high temperatures.

Thanks for the reply. The temperature in the air-conditioned house is in the low 70's to mid 60's.

Looks like a healthy plant to me. I wouldn’t worry about it. Maybe just a bit of sunburn…

I've recently had similar issue with leaf tip burn on my oncidium twinkle and gold dust and I was using tap water with PH around 7. After I posted on the forum and based on feedback I recieved switched to rain water or RO water and that seemed to help stop the browning leaf tips. Also I havent had good success with using fertilizers like miracle grow and better grow brands. They increase the pH further. I have done pH testing on our tap water.with added better grow 11-35-15 fertilizer and it raised the pH quite a bit. I used.to have discoloration along the.edges of phalaenopsis leaves which stopped after I switched to repot me fertilizer.

Looks healthy to me too. Oncidiums do tend to get ugly leaves. One thing that you do have to watch... these need to never dry out. If it is tending to get dry between waterings, water more often. The fertilizer shouldn't be a problem, being very dilute.

Raised, made more alkaline, or lowered, made more acidic?

sorry I meant lowered i.e more acidic

I think sunburn is something to consider but overall I think your orchid is lacking nutrition, especially Calcium.

The fertilizer that you use is very low in micronutrients and contains no Calcium and no Magnesium.

The 30 ppm Ca in your tap water might not be enough and might not be consistent, most RO water fertilizers contain about 60-80 ppm Ca when feeding at 100 ppm N. So your tap water is "at best" providing 60 ppm CA a week. Then what about Magnesium? And does it have the same amount of Ca and Mg at every watering?

Finally, there's the question of Chlorine and how that is affecting the root zone. Some plants are really sensitive to water chlorination.

If you continue using tap water, you might want to try Peters Excel Cal-Mag or the MSU fertilizer for Well Water. Adding CaliMagic from General Hydroponics at about 0.5 tsp/gallon to your current fertilizer regime could help too

Any chance fungus?

Note that this thread hasn't seen any activity since early November...I suspect that the problem got solved.