Phragmipedium Cahaba Glow old growth looks poor

[magmachamber]

I have a Phragmipedium Cahaba Glow which is blooming for the third year. Every time the new growth matures, the old growth turns yellow and gets spots.

It is about to go into bloom now, and I will repot after it finishes.

It receives 13 hours of light at about 5000 lux. I water it thoroughly 4 times a week. The room it is has good air movement and kept at about 55% RH.

Any suggestions? Is this normal?

Thank you.