Newly purchased Cattleya leaves and pseudobulbs turning yellow

[Jeremy T]

Hello everyone. I am new to the orchid hobby and have been doing well with phalaenopsis. I have recently decided to stretch my wings and try a cattleya, and humbly in need of some help.

So, 4days ago I bought my very first Cattleya(Rth Shinfong Little Sun x Rlc. Hsinying Sunbeam/Youngmin Golden Boy) at an orchid show. It has 7 "healthy" looking pseudobulbs ; 2 with blooms (5 in total) and one with 3 buds. The pseudo bulbs with flower/buds are super"fat". I must admit I didn't do a thorough check on the condition of the plant before purchasing it. The flowers were a bit damaged but I felt can sacrifice the already bloomed flowers for a pot with 7 pseudobulbs. All other pots have only 3or 4 pseudobulbs.

I kept my new baby 2feet away from a south east facing window. 24 hrs later I noticed that 2 of the pseudo bulbs and it's leaves have turned yellow. The following day another leaf and pseudobulb has turn yellow too.

Not knowing what I'm facing, I removed the sphagnum moss that it came with and thoroughly sprayed hydrogen peroxide (left for 5minutes), followed by listerine(as fungicide). The moss smells of mold too.

Once I've removed the media, I could only see a half cm of green root and 2 white roots. The rest feels dry, mushy and some are hard, but they are all in brown colour.

I haven't repot it and I let's it dry out overnight. After that I let the bare roots soaked in very diluted " CalMag" + Epsom salt for 4hrs.

Right now 4 of the pseudobulbs (and part of the leaves) are yellow. I am wondering if my plant is dying from my care or it has some fungal/bacteria/virus infection?

I have attached a few pics of this 5day old baby under my care. I would be grateful and appreciate some advice on what I can do next to safe my very first Cattleya. Thank you.