My bonsai tree recently just started loosing leaves not only the older ones but some fresh ones are falling off too (theres is yellowish transition, also some brown spots on the older leaves). At first i wasn't that worried cause i thoght maybe there was some watering problems. But now i just discovered more problems.
Tiny little white spots(bugs) on and under the leaves. Also the undersides of the leaves are reddish? (a reddish layer) Also the leaves are very lustreless (seems like theres dust on it)
PHOTOS ARE IN THE ATTACHMENT

Thank you in advance for your help

(Sorry for my incorrect English)

This is not a bonsai. I suggest you try and find a forum for common house plants.

en.wikipedia.org/wiki/Spider_mite

Treat with a spray against mites. Then, keep the air moisture content up. these are indicative of poor growing conditions. Dry air specifically.

leatherback wrote: Then, keep the air moisture content up.

Would spray misting every day or so do that?

I had similar problems last winter. The humidity was usually over 40%, which is pretty low around here. Three days it dropped to 30%, but over 60% maybe a third of the time. Would the plants think that that is low?

They are in the room with the tropical fish tanks, which act like humidifiers. I track humidity because of the guitars in the same room.

These plants naturally occur in regions with a humidity of 80+%
So yeah, 30% is not good enough.

I will repeat it once more: Growing bonsai indoors is a bad idea unless you are willing to invest loads of money to create the proper growing conditions.