Bilobed Grewia spots

Hello everyone.

I recently purchased a small Bilobed Grewia along with some Hokkaido Elms from a local nursery with the intent of growing them indoors over the cold months as I live in a 6a/b climate and they were kept in a heated greenhouse over the winter at the nursery.  I was told by the owner of the nursery that these do not go dormant due to the way they were grown, so I don't have to bury them with my other trees over the winter and instead keep them indoors under lights when it's cold outside.  I don't have any experience working with either species of tree, but they looked interesting and I need to have something to look at and ponder over the next 5 months before spring comes around.  

I've read that the elms can be hardend off for the winter and would benefit, but I don't want to risk it just yet, and that's a topic for another forum.  We'll see how they feel after this winter.
 
I have my sub-tropical and indoor trees growing under 4 t5 HO bulbs  at 6300k with a couple LED panels to spice things up.  They lights are on for 14hours. It's approx. 18-21c (64-70f).  In an attempt to keep the humidity up all the trees sit in drip trays with lava rock. I water all my trees individually depending on soil/tree.  It's my first year running this setup, and I think they'll be happier here than near a window.  In the summer they go outside.

The Bilobed Grewia sits in a small 4"x4" pot and was trained and pruned from early on by the nursery. It sits about 5-6" tall.




I noticed recently some small black spots appearing on the leaves and some young stems, and some of the leaves look like they were being eaten. The leaves range in size from 1/8- 1/2".





This is worrying as new leaves that are just opening are appearing to be already damaged.

Is this a fungus?  Is it a bug?  I inspect every day, or at least try to, I sometimes see what looks like aphids on the underside of the pot, but I "crush them with my finger",  I haven't used any insecticides or neem as it's only 1 or 2 or sometimes none.  I havn't found anything on the underside of the leaves.  

Am I over watering?  The soil it sits in is the nursery's organic bonsai mix.  Same thing my Serissa sits in.  It retains moisture for a good 3-5 days.  I plan on repotting it in a 50 organic 25 lava 25 haydite mix, and would like to repot it sooner than later although I'm pretty sure I should wait till spring with that?... ...

Is it a deficiency?  I hear that Grewia's like an acidic soil.  Should I use some Ferrous Sulphate?  

I also have noticed leaves yellowing quicker.  But that once again could be just acclimatization, or their natural cycle, or some evil spirit that doesn't want my trees to succeed.  Either way, if anyone has any thoughts, it would be greatly appreciated.

Thanks for your time!

I cannot specifically answer your question about cause, but there are others here who will nail it down for your with their voodoo magic pestological knowledge. I am responding because of some similarities I noticed. The first, that does relate to your problem, is that my wife bought me a bonsai locally and surprised me by having it in my 'plant room' already. I was surprised and did not stop to think to quarantine it from the rest of my tropicals and treat with neem oil a couple of times. Now sure enough I have little flies that remind me of fruit flies, and growing tips are suddenly turning black on a few plants. Now I get to neem oil everything. Nurseries are wonderful for adding to a pest collection. The other similarity, just purely as a by-the-way, is that we seem to have a similar setup- T5 bulbs, 65-70F, drip trays. This year I added rabbit hutch bases to better contain water spills. Plus I have a room humidifier and a fan for circulation. Most of the winter, that room's humidity is 55-65%, though during significant cold spells it can hover around 45-50%.

Good luck pondering!

Looks like leaf miners to me, but they're only unsightly. Remove and destroy the leaves.

@Precarious We do seem to have a similar setup although my humidity levels hover around the 40-50% mark thanks to central heating. I might invest in a cheap humidifier for my trees, if it makes a difference in their well being. Since your post, I did treat all of my indoor growing lamp trees with neem, yet today while inspecting I found those buggers in my lava rock humidity tray. I think I might have to re-treat my trees, sterilize the rocks, and clean the tray. We'll see what happens. Too bad this is the busy season at work or else it would have been done many days ago.

@JimLewis As per your jedi wisdom (I noticed you have many knowledgeable posts here so I take your suggestions with more than a grain of salt) I picked off the ill leaves. I probably took off about 25% of the total foliage. I noticed new growth over the week, and a much decreased rate of the black spots and snacked on leaves. I hope that diligence and continued leaf picking/neem spraying will finally give the Grewia a chance to bounce back pest free.

Thanks again for your feedback gentlemen. Much appreciated.