Hi this is my first post so I will try to draw you all in!

I have a Lagerstroemia Indica (Crape Myrtle) as a bonsai, its kept indoors next to a large south facing window which is usually open. (I live in the south east of England)

I have a problem.

The leaves are turning first red then to brown around the edges and then turning and curling up and dying, this is all leaves new and old.

There is also appearing on some of the older leaves a sort of salty/gritty substance near the tips which is rough to touch and appears to be part of the leaf, not really dicoloured either.

All the new leaves are growing on leggy stems and are dying off before they turn green and staying more of a yellowish colour.

Has the tree got perhaps a deficiancy of some form, maybe Iron or Manganese? Too much salt in the soil?

I am unsure and have re-potted it in fresh mixed soil/akadama for fresh nutrients and have started to mist the tree.

I would be very grateful for some information on what this might be and thank you all for reading my post.