Calculating Rock displacement
 

Any good rules of thumb for calculating how much water rock displaces?

I'll be dosing a product that says do not overdose. Calculate "exactly" the gallons of tank water.

It's for algae-x. Which still wont arrive til Wednesday. Wish I knew the vendor was on holidays. I would have beat my Dino's by now.

With live rock varying in shape and density I think displacement in water would be the only row me way unfortunately. I have always guessed and then confirmed based on my dosing. Calculate how much is required to raise alk etc for your guessed volume. Based on what it measured after you can know if you guessed high or low.

Only sure way is to use Archimedes' principle.

http://reef.diesyst.com/volcalc/volcalc.html

And don't forget to account for the water in the sump as well.

I this will be very helpful. Thanks. Good starting point and makes sense.