Cant open the picture. Can you post here?

While Chinese Elms can be grown indoors, they don't like it, especially if it spend most of it's past outdoors. Even in a shallow bonsai pot they are hardy to zone 6, -10F. Mine are outside all year, and have been fine down to our low of 12F. How long have you had it? These are often mass produced in China and shipped with pebbles on top of a dense clay soil and develop root rot if not repotted into good fast-draining bonsai soil. Rather than submerging, pour water over the surface and you should see it coming out the bottom right away, almost as fast as you put it on.

When using a homemade insecticidal spray always test it on 2-3 leaves first to make sure the tree is not sensitive to it, and if applied in the sun the acid from citrus could kill the leaves. For aphids, I just use plain water, spraying it knocks them off into the sink or ground but a few drops of mild dish washing soap in it is OK too.