I was curious about actual water volume before I start doing any kind of dosing.

I have a standard 90, but with sump and fuge I figured I was at about 100g of actual water volume. I knew there would be some displacement from rock and sand, some extra volume in plumbing, etc. I was surprised when a system volume calculator put me right back at 90.1 gallons.

I used this calculator:
http://reef.diesyst.com/volcalc/volcalc.html

Anyone use this one, or have another one I can try to compare?