Great reading over the weekend fellas!
I'm going for moler clay @ 65P per litre will do a controlled test in distilled 2ltr plastic bottles.
As for salts Ive got to try and mix a decent solution and see if they will obsorb well but being clay it should and then bake it till it tries, only question is controlled environment testing?
1) Stick four plants into the same tank with filter running no fish!
2) Stick one each into the tank, but that would take me about two to three months for any results?
3) Leave them in the open air, but fill the distilled bottles with just tap water?
I can cheat and buy some Osmocote