Are the crystals you have purple-ish in color? I found a little goes a long way. I mixed them in by the teaspoon, maybe 1tsp per half cup of water? That's really a rough estimate, dump some in, see what you like, then add or subtract.
It's weird, they're purple, and don't have any smell... then you add them to water, the water turns amber in color, and smells just like home brew aquafortis.
If you use too much of the crystals, I did find it muddied the grain a slight bit, but didn't make things significantly darker.
Here's a photo of my first rifle 6 years ago, I cringe that I'm posting this online... This had two or three coats of the stuff, because I wanted darker, but didn't have real aquafortis at the time, and didn't know about LMF analine stains either. One coat alone is lighter than the stock shows. I used one light coat on a pistol I'm finishing up, I'll snap a photo of the base color and post it tomorrow.