Repotting for species Phal?

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What are your temperatures and humidity? This is a warm-growing, humidity-loving species.

When you say poor medium, do you mean old or something else?

Phals usually carry more leaves in warm, humid greenhouses than in cooler, less humid homes. Often they will drop a few leaves as they get accustomed to a home.

The white deposits on the pot are probably from minerals in your water, not from the medium. Do you know the water quality report for your water?