I reported one of the tropicals last September, using akadama, lava rock, and pumice, so the top of the mixture has quite a bit of white pumice. Well, it used to. I fertilized it with Miracle Gro, which dissolved into a blue mixture and since October the top of the mixture has had a lot of blue in the middle and white on the edges.

I thought it would rinse out in a month or so. Nope, it is just as blue now as five months ago.

How do you clean out pumice?

I guess I could dig out the top layer, replace it, and then inject future fertilizer below the top layer. Something easier?

I have the same problem here when fertilizing with MG if the soil has a mix that uses white DE.
So I solved the "problem" adding an extra layer of lava+akadama as a top layer.

Or you could stop using Miracal Grow!!