You have a Miltoniopsis. Considered difficult by orchid growers in Sydney, Australia.

Where are you in the world and what are conditions like in your home where you have the orchid?

San Diego CA. AC controlled at 76 degrees and on the dry side but I mist the top of the moss when it turned dry to the touch. Deeper watering once a week.

The other psudobulb is heathy and growing lovely flowers as you can see. So it probably isn't the soil that is the problem.

started to die when it arrived at my house?

==>>> explain what this means.. mail order.. florist delivery.. or you brought it home??

and when did all that happen ...

if mail order.. and recent ... then talk to your seller ...

moving from one place to another can be very stressful... can we define those stresses ...??? .. could that flower stem have been damaged in transit???

im not sure misting is doing anything... but i dont grow orchids to know if that is a thing ... are you accomplishing anything other than moistening the surface of the moss.... and do you think once a week watering is enough.. or too much.. how do you know.. who came up with this schedule for your house .. how do we know its proper ... better to learn how to check. rather than rely on random schedules...

your plant is flowering.. and otherwise looks pretty happy ... lets not try to fix what might not be broken .. and screw it up ...

ken

My post has multiples psudibulbs and I don't believe they are of the same variety. I purchased them from a store and in an earlier purchase, two psudobulbs in the same spot yielded two different color/pattern flowers.
I want to.know if the sick one is caused by infection. Because I want to minimize the risk of infection spreading to the other two health psudobulbs.

I have grown a miltoniopsis successfully for the past 4 years that i picked up at trader Joe's. I picked up two more a month back or so, from the same place in essentially similar potting set up to yours. They were labelled "exotic orchids." :) Anyhow, the current lot were in way worse condition root health wise than my previous purchase. Since they were in bud/bloom I tried to postpone repotting until after blooms were finished but unfortunately the buds were already failing one one and stalled at half open stage in the other. I bit the bullet and checked the roots. They were potted up in fine bark and sphagnum mix with some finer/broken down material that looked like potting mix. Although the roots and stiff at first, after unpotting and washing they all seemed mushy, rotten or hollow. There were very few viable roots.

My experience with miltoniopsis repotting is that any live/viable roots also turn to mush promptly after repotting in such situations and only new root growth eventually survives. Anyhow, I lost the buds booms despite the repotting procrastination and soon after repotting as also all of the roots. For now, both of new acquisitions are "repotted" in coconut fiber (mostly rootless pseudobulbs wrapped tightly and stuffed into smaller containers. One has started growing new roots on an existing newish growing pseudobulb the other is hanging in there without roots for now.

Regarding two different colored plants in a single pot, I would say that was a random fortuitous occurrence unlikely to be repeated.

Miltoniopsis like it cool and thrive in cooler conditions. My advise - Try to keep the as cool as possible and away from any source of warmth. If you nights are cool leave them outdoors overnight. Repot as soon as the flowering is finished, sooner if the buds a a lost cause. Commercial growing for mass sale essentially involves hopping up the plants on fertilizer and hormones to get them to bloom to make the sale. While they are not the healthiest plants out there, I think at $20 a piece it is not a bad deal if one can save them. They do recover and bloom the next year if handled well. Despite several setbacks while I was teaching myself miltoniopsis culture for my conditions, my 2017 acquisition has grown from 5 pseudobulbs to probably 20 or so (it's a bushy thing with too many to count). Not many orchids grow that fast. Good luck.

And the roots do like to be evenly moist and not dry out between waterings. That means moist but not soggy - fine bark, tree fern, sphagnum or such. I have never been able to keep anything alive in sphagnum. Fine bark, perlite and moss mix did work for some time but it isn't a repotting friendly media and every time one changes to a different substrate the roots die, I have settled on coconut/coir fibers for the ease of potting and repotting without losing roots and providing adequate moisture without sogginess.

Just shock

Thanks everyone! You have all been so helpful! A quick update. I cut off the dying buds (9ne from.each spike both on top) and the remaining bud on the two spikes are now doing great. One is opening it's gorgeous face now!