But to my surprise the soil was full of black larvae under the moss. They were about two and a half centimeters of size and full black. I didn't know how they got there but as i cleaned, they kept coming.. It is Summer here in Turkey and wasn't the right time for repotting a Chinese Elm so i kept the soil.. He started to yellow gradually (i water once in 2 or 3 days..). I had to do something. When i checked entirely, i saw he was almost rootbound. Finally, prior to three nights, i repotted him. Cleaned every last bit of the old sandy soil. Used washed gravel and bonsai soil mix i bought from a bonsai shop. He is still yellowing.. Do you have any idea?
You should have repotted immediately, even if it wasn't the right time. The fact that soil that doesn't hold any water indicates that it has been dried out at some point in time, and has become hydrophobic. Without a photo I can't tell you what the black larvae were, but they're probably not a good sign and may have been eating from the roots.
You have already repotted. Continue to take good care of the tree, following the guidelines for your tree type. Check the soil for the return of the bugs. Hope and pray for it to recover...
(i water once in 2 or 3 days..)
Don't water according to a schedule. Water thoroughly, until water drains out of the drainage holes. Then let it dry, but do not let it dry out completely, and water again.