I went to Walmart and bought a tea strainer with a fine mesh. I just dump the GH booster in there and swish it around the water. It isnt dissolved but it comes out in a fine white cloud that settles on the gravel and disappears withi an hour.
The stuff that doesnt fit through the strainer, I kind of manually smoosh it through with my finger, and the stuff that doesnt even go through then, I just dump in and it dissolves within a few hours. But thats usually only a trivial number of clumps.