This is a followup to this question, from a couple months ago. I tried yesterday to edit that question to include the followup, but it was not very well-received -- I assume it was not the right thing to do, so I'm starting a new one.
While my citrus (key lime tree) is now making new leaves, some (3 or 4) of the "big" leaves are still looking unhealthy -- curling, with the edges turning dry and white.
I was not sure it was a big deal (after all, it is making new leaves), until I moved the pot today and saw this underneath:
I cleaned it and removed the white stuff from below, but now am pretty worried.
(I water the plant roughly 1-2 times a week, with nothing in the water -- I am no longer using "liquid plant food" as I used to every time ~2 months ago)