Chemically pure sodium tetraborate powder will assay as almost 200% chemically pure sodium tetraborate decahydrate because it can make that much decahydrate by absorbing water. You can look up the NF grade which has practically no soluble or insoluble impurities and you will find that as the decahydrate it will assay as between 99.9 and 110%. I don't know where you learned your chemical engineering, but I hope you didn't learn all they were teaching. Most reputable schools would be better than that.
You will not precipitate any water insoluble solids from technical grade borax decahydrate powder.
You are saying that if I don't filter my borax solution, it will have insoluble solids in it.