There are three kinds of TD...water soluble, oil soluble and can be soluble in either. Despite the directions you were given (you really don't need to mix with hot water), it could be that you have an oil soluble TD...hense the specks. Oh...I just saw that you are mixing it 1:1...is that 50/50 or is that 1 tablespoon water to 1 teaspoon of TD? But whether you use water or oil, TD is a mineral and thus is heavier than oil or water and will settle to the bottom...there is just no getting around that.
As for differences in brands/sources...IMHO, as long as you are buying it from a reputable company it's all the same. I've bought TD from two different soap suppliers and there was zero discernible differences so they probably bought it from the same wholesalers and then just put their label on it.
Lisa from "I Dream in Soap" has a video on
Mixing TD that is interesting. She uses a TD that is soluble in water or oil, but mixes her TD in oil as she finds that she can just stir the TD in to whiten/lighten her batter..no sticking required. She also pre-mixes a batch in one of those Nutra-Bullet things to really break down and combine the oil and TD. I'm thinking about giving it a try when I mix up my next batch.