How much water in my tank with live rock

[Richards Aquarium]

How do I figure out how much water I actually have in take with live rock and sand. I want to treat with prazipro. Also what do I need to remove from filter just the Carbon ? Looking for advice
Thank you.

 

[Lavey29]

Kind of comes down to best guess on volume. My 65g DT has considerable rock so I'm guessing 50g volume now. Take carbon out for prazi.

 

[Wave Whisperer]

I use this for calculating water volume.

Tank Volume Calculator

Make sure to measure out your sump as well. For height, use the current water height both for your DT and sump. Once you got that calculated, its basically down to estimation on how much to deduct based on your rocks and sand bed. Its better to err on the lesser dosage than overdose.

Take out carbon if using any form of medication that needs to be dosed to the tank.