dosing ???

[yousuredo]

well her go,
i know this is probably not a real big deal but need to know anyways.....

when dosing say PH/??? whatever and it tells you to do 1 spoon full for 40gl's of water........???
well how do you determine the amount of water ?
i have a 75gl tank and about 20gl sump-fuge......75+20= 95gl's
or do take the rock,sand factor and add that to the equation, i figure with my rock,sand in the tank it is more like 55gl's in it or so not 75gl's.....55+20= 75gl's
so does it matter ..........and if so whitch do i do

[Geoff]

i just guess.

i actually dose per the total volume of an empty tank. LR is pretty porous so most of it is filled with water anyway. if you want to be really funky you would weigh each piece of LR then figure out its water volume equivalent in weight. about 9 lbs per gallon. so it takes a lot of LR to make a big difference in doseing. your substarte would have a greater impact, but still not super significant.

G~