5 yo sweet plum leaves yellowing

[6unnie]

I am new to bonsai and ordered a 5 year old sweet plum. I don't have a good window to directly put my plant in so it sits against a wall close to a window with a full spectrum light bulb on.. I keep the humidity tray filled and occasionally add water to the top of the rocks. Previous owner gave instructions to water ontop of rocks if they are light, and to keep the humidity tray filled.

I have owned this sweetie for about a week and leaves already turning yellow which is scaring me as I don't want to kill this plant.

I know there can be stress when the plant is moved.
After reading on this forum, I learned that the sweet plum is an outdoor plant (although the seller labeled "indoor"). I don't have the option to put outside because I live in zone 5.

Does anyone have suggestions to keep this plant healthy indoors?

I feel the seller didn't fully disclose how to care for this plant and I clearly didn't do enough research on my end. I don't want my sweetie to get worse.

I keep my house at 73F indoors. I can also use a humidifier if needed. I have little sprouts growing from the top of the rocks, I am not sure if this is good or bad.
Any suggestions would be greatly appreciated, thank you!

 

[TimberLakers]

Here's a high level care guide for your tree: link

My guess would be that it isn't getting enough sun, or lightbulb in your case. If it's looking for 4-6 hours of sun in the winter months - your full spectrum bulb might be insufficient.

Would try to get your tree into a natural light source.

 

[6unnie]

Here's a high level care guide for your tree: link

My guess would be that it isn't getting enough sun, or lightbulb in your case. If it's looking for 4-6 hours of sun in the winter months - your full spectrum bulb might be insufficient.

Would try to get your tree into a natural light source.

Thank you so much for that info!