Not to answer this question, but more along the line of a "universal defluffer", when I did (re)crystallizations, I always looked at the crystals with a magnifying glass as soon as they began to form. If I saw amorphous solid, I took that as a signal the solid is not pure. I might filter with silica gel or charcoal as needed as one remedy. I expect pure substances to form hard crystals. I cannot say that is a rule, but it seems generally true. (I never succeeded in getting good crystals of dibenylacetone though the NMR spectra looked pretty good. I suspect a small amount of a geometric isomer is preventing good crystal formation, that is pure crystals.)
I shall assume that because a fluffy solid is forming, that it is not pure. In this case, I can image that different salts of calcium might be forming and resist forming nice crystals.