Heart broken sick Miltonia. flavescens

[Zoi2]

I don't think that's salt build up, it looks to me like fertilizer burn and media kept too wet.

I have both oncidium and miltonia in s/h and they are doing wonderfully, as long as the pots are flushed routinely and you don't let the leca dry out salt is not an issue.

I would not advise transferring this plant to s/h until new roots are actively growing.
Joann