2nd last phal leaf turns yellow

[KC Kam]

Hi All,

I have a phal where its 2nd last leaf turns yellow. As far as i know, phals dropping its oldest leaves are normal. But my phal's last leaves were fine but the 2nd last leaf is turning yellow. Regarding its health, it is growing roots, new leaf bigger than the previous one and also developing spike.

Any idea why? Is it due to insufficient nutrients due to its current rapid growth?


Thanks.