That is one issue with the powder that it is difficult to emulsify into the water.
As long as you do not over dose from the amount.
That is where you need to be specific and the "ah, that looks about right" way of measuring will kill shrimp and snails if too much. With your scale you should be fine. I can in no way mathmatically calculate a safe amount in the dog dewormer. So I would not use it even if it did mix easily, lol!!!
It is the same medicine. Though I don't know what the other ingredients are, as in the, non active ingredients like stuff to hold the tablets together, binders, etc. As Phoenix killer said, [paraphrased] I can't make a claim something works if I didn't use it. I am not one who used the powdered pills, but many people have positive experiences.
I can say that the Safeguard Liquid Goat Dewormer was like magic. After weeks and weeks and weeks of frustration. Bliss.