Total Water Volume for Water Changes?

[ReefBug]

I have a 24 gallon nano. In it is 28 lbs live rock and 30 lbs live sand. An additional 3 lbs live rock rubble is in the filter chamber.

This brings my REAL water ammount to 18.5 gallons.

Is a 20% water change for this tank then (approx) 3.7 gallons, 20% of 18.5 or, 4.8 gallons, 20% of 24 gallons?

After all my years in reefing, it just dawned on me that I have been doing 20% of the total volume. Not 20% of the real volume.

Which is actually correct?

 

[brian is cool]

i have a 20 with a 10g sump and i do 5g water changes

 

[Fish'InMN]

I've seen posts like this a lot lately and I think some people are taking this "20%" rule way too seriously. Just find an amount that you can easily measure and make.

I have a 15g nano and I do water changes of 16 quarts because I have a pitcher that holds 2 quarts and its a good amount of water in a 5 gallon bucket. Add 3 and a half cups (not real cups in my case, just an old plastic drinking cup) to make 4 gallons of water at 1.026 salinity.

 

[ReefBug]

Thanks for the replies.

I'm not asking for an exact amount, just if whatever amount you choose to do should be based on the entire volume of REAL water in your tank, or, the total capacity.

I'm not concerned about my water changes. I do 5 gallons bi-weekly, 2 1/2 every 3 days. I, too, have a purfect 2.5 gallon bucket I use that makes this "chore" comfortable.

I am mainly just curious.

Anybody else?