# How to calculate volume of the LR?



## sig (Dec 13, 2010)

Let's say tank is 150G and has 170Lbs of LR. what is the clean volume of the water in gallons do I have.

I tried to calculate, but I think something wrong here. Any opinion

1 kilogram / l = 8.34540445 pounds / US gallon
So live rocks 13.4 - 14.2 lbs per US gallon

I have 170 lbs= 12.0 - 12.7 gallons

http://www.aqualogo.ru/living_stones

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## Shoryureppa (Jul 1, 2011)

Rocks have different densities so a small rock can weigh much more that a large one that it porous. I'm assuming you want to calculate for dosing purposes. I got an advice once to measure the amount of water that I initially put in to make dosing easier. I have 135lbs of rock, 125 lbs of rock and a 40 gallon sump and the water volume is 107 gallons. It is also difficult to calculate because the sump is not completely filled


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## Redddogg69 (Oct 1, 2011)

The easiest way to do this (and most likely the only possible way) is to mark the water level in both tank and sump, then remove the rock and add water (measuring as you fill) to the marks and record how much is added. The rock will displace water based on size rather than weight.


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## cablemike (Jan 7, 2009)

there is an even easier way, just remove 1-2 buckets of water and measure how many inches the level dropped.. if its like 2 inches and the tank is 20 inches high subtract the nomal inch or so which is where the water line sits blow the top also.. so if its 20 inches tall it goes down 2 inches , there is an inch above the water line and you have 3 inches of sand you would end up with 14 inches of water remaining we know 2 inches was removed totalling 16 inches of water. the two inches filled a 5 gallon bucket. so each bucket takes two inches devided by 16 total inches is 8. 8 buckets time 5 gallons is 45 gallons of water more or less, and since the sand bed isnt completely solid im sure it has no more then a couple gallons of water that are actually saturating it. so you could say 45+2 to be safe for 47 gallons of actual water. make sense? im real tired so please forgive me if this doesnt make sense. i know when i shut down my 90 it had 55 gallons of actual water in it because we took it all and put it in buckets.


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## Redddogg69 (Oct 1, 2011)

Cablemike wins the math award lol. Just reading that made my head hurt like in high school, but then again in those days I put the high in school.


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## altcharacter (Jan 10, 2011)

Or you could have measured how much water you put in when you setup your tank...like a few weeks ago...but you didn't think of that right?? ;p


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## sig (Dec 13, 2010)

Thank you guys and i think Mike is the winner 
Thanks again

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## Dax (Sep 29, 2010)

Can I be the new Winner? There is a even easier way once you find the right tools. Here you go:
http://reef.diesyst.com/volcalc/volcalc.html

Unless you know the density/porosity of the rock, its weight doesn't accurately give you a relationship to the volume it displaces. The ONLY way to accurately measure the volume is to either remove the rock and see how much water is left (l x w x h), or remove the water and measure it.

If you really want to figure it out, get a bucket, mark lines at 1 litre intervals, fill it half way and note the water level. Now take one rock and place it in the bucket. The water level will move up by the amount the rock displaces, which you can figure out by looking at the lines you marked on the bucket. If you do this for all the rock you can add up the numbers and subtract it from the volume of the tank. TA-DA.

To get a decent ballpark figure, instead of doing all the rock, just take one, weight it, see how much it displaces and then if you know the weight of the rest of the rock you can calculate it from there.


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## sig (Dec 13, 2010)

Dax said:


> C
> Unless you know the density/porosity of the rock, its weight doesn't accurately give you a relationship to the volume it displaces.


thanks man. unfortunately you can not read in Russian, but in the link provided they already measured density/porosity of the rock (wet rock live rock)

this is used in my calculations above

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## Dax (Sep 29, 2010)

sig said:


> thanks man. unfortunately you can not read in Russian,




Getting the density of the rock is a guess at best, but let's say your numbers are correct. If I use the lower density and read it as 13.4 lbs of rock will displace 1 gallon of water, then 1 lb will displace 0.0746 gallons (1/13.4). Now multiply by the number of lbs of rock (170lbs) and you get 12.7 gallons. There you go, your calculation is correct.

I also used the link I sent and put 0 lbs of live rock to get a volume of 150 gallons. I then added 170 lbs of live rock and the tank volume went to 138 gallons for a difference of 12 gallons.

Happy now!! You're a smart guy, why do you doubt yourself?


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