Originally Posted by smokingreefer http:///forum/post/2670067
rule of thumb is 1-2 lbs per gallon
+1 - But it really depends on what type of rock. Some are more dense than others. What is really important is that it works in the space you have. Don't overcrowd your DT just to meet the "minimum" LR quota. You can allways put some in your sump too! -Another good reason to run a sump.