I think you've been doing a little too much topekoms! (My team name in highschool some 25years ago)Reef crystal and io are terrible I would wait out for the tropic marin
I've been using regular IO for the last 8 years and it mixes clean. I haven't cleaned my 100g storage once.
And Randy uses regular IO. If it's good enough for the preeminent chemist, it's good enough for lowly old me!
Normal IO has no brown sludge and is what I used for 20 years. Reef Crystals does, and I suspect it may be the result of the vitamins and metal chelators they add (normal IO does not have these).