I don't pre-dissolve. I sprinkle a dusting of the gelatine over the surface of the finished, reduced product, let it bloom a bit and sink then keep doing that until there is no more, wait a few minutes and stir with a wooden chopstick (or plastic) so that there's no temperature differential so none of the gelatine that might not have fully dissolved sticks to it, give it a good stir and call it even.
I believe (I'm sure the info is on the forum somewhere) that Kephra and others pre-dissolve the gelatine in cold water, letting it bloom for IIRC something like 5 minutes and then just add the correct amount to the finished Colloidal Silver.
It can even be stored in the fridge but I suspect it will soon start evolving life so its lifetime as a solution is limited. Again too, this has been discussed on the forum somewhere and since I don't do it this way, sorry, I couldn't direct you.
If you're adding dry powder, you have to do it gradually because if it clumps, the clumps most likely won't fully dissolve.