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Old 10-27-2004, 08:11 AM   #1
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LR Displacement Ratio

Just wondering if anyone has an idea or experiment results on this one...if you're adding the typical 1.5-2.0 pounds of LR per gallon, what percentage of potential water would be displaced? Now before everybody comes back saying, "it depends on this, it depends on that," let's say it's 1.75 pounds of LR per tank capacity gallon and the LR is from LR.com. For example, let's say we're talking about 175 pounds of LR.com LR in a 100 gallon tank with a 3 inch sand bed, about how much is the true remaining water capacity? TIA.

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Old 10-27-2004, 08:47 AM   #2
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Well I had my tank full of water and brought home 60# of LR from LR.com last week. I didn't make a note of it but I believe it was about 5 gallons that I had to take out to keep it from overflowing upon placing the rock in the tank.

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Old 10-27-2004, 08:53 AM   #3
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To get all mathematical... a gallon of saltwater weighs 8.5 lbs. We know that the rocks are more dense than the water (otherwise they'd float) so a gallon of rock would weigh more than 8.5 lbs. So my displacement of 1 gallon per 12 lbs of rock sounds about right.
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Old 10-27-2004, 09:44 AM   #4
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Really the only way to determine this is to measure the displacement directly. Remember the displacement measure is a factor of how much mass the rock has not how much it weighs. If you really need an accurate measurement, you could calibrate how much your water moves when you add 1 or more gallons of water with a marker on the outside of the tank. Once you have that (say for argument sake it moves 1" then when you add the LR, you can measure how much your level moved from start to finish and you will have a pretty accurate idea of how many gallons equivalent was displaced. This will allow you to determine the new 'capacity' of the tank with the LR in it. Hope this makes sense.
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Old 10-27-2004, 10:01 AM   #5
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A ROUGH estimate says that limestone weighs 2000kg/m3. LR.com rocks are limestone based. If you convert that to English units its about 16lbs pre gallon, taking that a step further for every 1lb of LR you will displace 1 cup of H20. Keep in mind these are very rough numbers and are subject to many variables.

You could figure sand the same way if you knew the density of the material.
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Old 10-27-2004, 10:51 PM   #6
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u cant really got by wieght when u are dealing with rock because some rock is more dense than others ...it is all to heavy to float therefore to really be accurate u would have to go by the surface area of the rock which is gonna be **** near impossible unless u have a squared rock
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Old 10-28-2004, 11:23 AM   #7
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actually not really ... fill a bucket (or your tank) partway and mark the waterline. add rock. measure how much the water level rises. calculate how much water is displaced.

it's the most effective way to measure volume (and by calculation, density)

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