I bought this... http://www.growell.co.uk/p/0123/Manual_pH_Testers.html

Ph means.... acid & alkaline... u need to neutral them out.

If it is too high OR too low u add... http://www.growell.co.uk/p/0128/pH_Up_and_Down.html

I dont use it though... I find if u boil it & leave the water overnight your PH will be perfect instead of messing around with these chemicals. PLUS ITS CHEAPER !!!