newb with water volume question

[satellite62]

I note that most of the threads deal with tank size and not with actual water volumes.

I have a new 75 gallon with a 30 gallon sump. I have 100 lbs of LR and 80lbs of LS in the main tank and 5 lbs of LR and 20 lbs of LS in the sump/fuge. I assume that the LR and LS is displacing at least 15 or more gallons of water.

Should the calculations for adjustments for salinity, calcium, ALK etc, be based on this lower water volume figure? And would this also determine the pump size needed for the exchange of water between the two tanks?

[Zestay]

well for dosing your tank.
i always underdose my tank and check the test kits to see if it does enough. to be safe i would dose my tank as a 75 gallon tank. and any serious medicine dosing would be done in a seperate QT tank.

the pump size i wouldnt worry about to much because your going to have headloss ( gravity! ) fighting your pumps so i would assume your tank would be at full volume while selecting pumps.