Odd color on side of top soil

[BigBallerBonsai]

I noticing some oddly colored formation on the side of the top soil on my Chinese elm. Does anyone know what this is?

 

[TomB]

Mineral deposits. Could be from hard water, or fertiliser salts buildup. Often a sign of a tree that's being kept inside and over watered.

 

[BigBallerBonsai]

Mineral deposits. Could be from hard water, or fertiliser salts buildup. Often a sign of a tree that's being kept inside and over watered.

Thanks! Is it harmful for the tree? Does it also mean I am fertilizing too much? How would moving it outside affect the amount of minerals in the soil?

 

[TomB]

I think this was answered on your other thread