Not very much. Just a teaspoonful in a medium sized pot. Or try soaking a teaspoonful to see how large it gets, then mix it in well. If you put too much in it swells up and looks as if the pot is erupting with frogspawn!! So slightly underfill the pots if putting it in dry.

I try to keep the crystals near the bottom of the pot - it's where you want the roots to be and they look weird if they get to the surface. So I use compost without any crystals for the top third or so of the pot.

Follow the instructions n the packet....