Displacement Calculator

Karen00 · Jun 28, 2021

Hello fellow saltines,

I saw a few threads lately of people asking for help with dosing copper and were asking for guidance on how much to use relattive to a tank's volume. @Jay Hemdal pointed out that dosing is based on the tank's displacement volume. I am so glad I read these threads because I wouldn't have thought of that. I'm in the process of starting my 5g build and want to get this figured out before everything is in the tank. Are the two primary weight factors sand and rocks? I can't think of anything else.

Also, I came across this fairly robust calculator. http://reef.diesyst.com/volcalc/volcalc.html. Has anyone tried it? Note: The page isn't phone friendly so you have to do a bit of pinching and expanding of the page. Haha.

Thanks!

Jay Hemdal · Jun 28, 2021

Karen00 said:
Hello fellow saltines,

I saw a few threads lately of people asking for help with dosing copper and were asking for guidance on how much to use relattive to a tank's volume. @Jay Hemdal pointed out that dosing is based on the tank's displacement volume. I am so glad I read these threads because I wouldn't have thought of that. I'm in the process of starting my 5g build and want to get this figured out before everything is in the tank. Are the two primary weight factors sand and rocks? I can't think of anything else.

Also, I came across this fairly robust calculator. http://reef.diesyst.com/volcalc/volcalc.html. Has anyone tried it? Note: The page isn't phone friendly so you have to do a bit of pinching and expanding of the page. Haha.

Thanks!

The best means to determine the actual volume of small tanks is by directly filling them with a measured volume of water. For larger tanks, you might be able to weigh the sand and rocks, and then guesstimate that they will displace about 1/2 that weight of water. In really large tanks, I just estimate that the rocks displace 15% of the water volume. Don’t forget to factor in the volume contained in the sump or filters.
Jay

Karen00 · Jun 28, 2021

Jay Hemdal said:
The best means to determine the actual volume of small tanks is by directly filling them with a measured volume of water. For larger tanks, you might be able to weigh the sand and rocks, and then guesstimate that they will displace about 1/2 that weight of water. In really large tanks, I just estimate that the rocks displace 15% of the water volume. Don’t forget to factor in the volume contained in the sump or filters.
Jay

Thanks Jay and thanks for mentioning sumps, etc.!! I wouldn't have thought of those either (the joys of being a newb). That calculator I posted a link for has sumps, refugiums, etc. as well as different shapes tanks. That's why I thought it was quite robust in its functionality. You're right that I can start to do the measuring of my 5g while filling the tank given it's a new build. I also want to try and figure out the volume of my freshwater tanks as I'm sure some of those meds also rely on the displaced water volume.