spidersweb, would it not be too concentrated testing like that? Wouldn't you have to calculate the volume of water in the tank and the amount of substrate to be used to make it relevant to the bucket size and how much test substrate you put in the bucket? Sorta slept through science class at school, but if you had 3kg of acidic (for arguements sake) substrate in an 8L bucket, and 3kg of the same subsrate in a 200L tank the pH reading on the tank would be less than that in the bucket? :-?