Live rock vs water displacement

[bontrager]

I'm getting to start a Inovative Marine 20 gallon aquarium. How much water in gallons will be displaced once I add 20 lbs or rock to it. Don't want to dose at the 20 gallon amount when it now holds less water.

I have the rock in the tank now it it looks like it taking up 50% of the real estate???

Thank you!!!!

 

[Marlon2024]

Considering water weighs 8.3 # I think or somewhere close to that o would say 2.5-3 gallons of water displacement I think. Not sure if my theory is correct but makes sense since 8# of water weights the same as 8# of rock

 

[AdamNC]

Easiest way is place all your sand and rock first then measure how much water you've added. My tank for instance is a 29 gallon. After setting the rock and sand I got lucky by adding exactly 20 gallons of water.

 

[bontrager]

Thanx to the both of you; makes sense!

 

[Grey Guy]

Since it’s a small tank you could take out the rock, fill the tank to top level. Drain down top 3 “ measuring what came out. Then add the rock and drain more water until all rock is in and tank is at top level. I think you’re asking a very important question. I’m going to look for a cheap water meter that I could hook to the fill hose.

 

[Dkmoo]

Considering water weighs 8.3 # I think or somewhere close to that o would say 2.5-3 gallons of water displacement I think. Not sure if my theory is correct but makes sense since 8# of water weights the same as 8# of rock

This actually doesn't work. This implies rock and water have same density, unless your rock floats in the water lol.

 

[Dkmoo]

I'm getting to start a Inovative Marine 20 gallon aquarium. How much water in gallons will be displaced once I add 20 lbs or rock to it. Don't want to dose at the 20 gallon amount when it now holds less water.

I have the rock in the tank now it it looks like it taking up 50% of the real estate???

Thank you!!!!

Depending on the density of your rock. Most rocks are either porous lime stone, sandstone, or calcified reef. Density varies but generally between 2000 kg to 2400 kg per cubic meter. Some rough math gets us to about 16 to 20 pounds per gallon. So if I have to guesstimate,I'd say your 20 pounds of rock will displace about 1 to 1.5 Gs

Sand, if aragonite, is approx 2.8g/cm3, that converts to approximately 22-25pound per gallon. In tanks the displacement us more on the high side bc the sand will never be "perfectly packed"

 

[Grey Guy]

Since it’s a small tank you could take out the rock, fill the tank to top level. Drain down top 3 “ measuring what came out. Then add the rock and drain more water until all rock is in and tank is at top level. I think you’re asking a very important question. I’m going to look for a cheap water meter that I could hook to the fill hose.

Another way. Fill the tank 1/2 full when empty. Use cubic inches to calculate the number of gallons. Put in all of your rock and measure how much water you needed to add or takeout.