Cherry Bonsai leaf tips brown and slowly yellowing then falling off

[Mskzuko]

Cherry leaves getting dark brown on leaves then eventually yellowing and falling off.

I purchased this little cherry (they did not specify spp but it was flowering when I bought it) in March (the first picture) and originally had it living outside but I think as the weather started getting hotter I moved it in to live on my north facing kitchen window. I water it usually every two days to once a week.

I am new to bonsai and new to plant parenthood in general - I feel like I've been making every generic new plant parent mistake in the book over this past year with my indoor and outdoor plants -_- if anyone has any suggestions I’d love some help on getting it healthy again.

 

[Deep Sea Diver]

The top leaves look good, the lower leaves look old and had some brown rot or cherry leaf fungus.

Best
DSD sends

 

[rockm]

You don’t say where you are. That important please post your location(country state) in your avatar at the left

If this tree is being kept outside as it should be and you are in a temperate climate like North America or Europe it’s nearing the end of summer. You should not keep this species indoors. It will die inside this winter next spring.
It is critical to get it outside and leave it there. Protect the roots in the winter. Look up overwintering bonsai online particularly what Bonsai Mirai posts on the subject

The cherry trees in my neighborhood are alll dropping significant amounts of their leaves as they do every year. Most are bare by the end of September