Magnesium and phosphorus deficiency?
 

What am I dealing with here? I don't know if it's one or the other or both. Please help and thank you

Cymbidium?

Looks like an aging leaf to me, or potentially something fungal.

If you have been providing any NPK fertilizer at all, it is not phosphorous deficiency.

If you are concerned about Mg, add 1/4 tsp Epsom salts to your water when you water.

It's a Zygo. Man I really hope it's not fungal, if it might be any suggestions on what it could be if it is. I am noting that it is just aging of an old leaf. I just think it is very odd since it just happened over maybe 2 days. I am feeding it a fertilizer that is very close to MSU, so it has cal and mg in it. I have also noticed a small purple streak on another older leaf and my gut is saying mg, but I am still very new at this. How long will it take to clear up if it is mg deficiency? Thank you

Zygos and Cymbs are prone to have ugly leaves.

Jess, I suggest you move nutritional issues to near the bottom of your cultural concerns. Light, water, temperature, humidity, and air movement are far more important.

I agree this looks like normal leaf aging, which can visually progress quite quickly when it reaches a certain point. And Ray is right - With appropriate use of an MSU type fertilizer with reasonable quality water in a bark mix, nutrients will never be the limiting factor in your success until everything else is perfected. Overt deficiency symptoms are extremely unlikely.

If you are using an MSU formula, you are very unlikely to be experiencing any nutrient deficiency that would require correction.

Per Ray and PaphMadMan's posts, nutrients are low on the list of cultural priorities. Not to be neglected completely, but the priority is not high.

I suspect the leaf is just an old one. As leaves age, their defenses are reduced, they are prone to getting spots, streaks, etc. and look ratty. As long as the younger leaves seem healthy, I would not worry overmuch.