is there a formula to calculate how much soil to use? - The Planted Tank Forum
Old 05-01-2012, 02:21 PM Thread Starter
Planted Tank Enthusiast

Join Date: Nov 2011
Location: Clarksville, TN
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is there a formula to calculate how much soil to use?

I am going to be converting my 46 gallon tank to a dirted tank with PFS cap, but I haven't any idea how much soil it will take for the task. Is there a calculation I can use that anyone can share with me, so that I may get the right amount from the get go and not want to kill myself later? I appreciate any help

Regards, Therese

Last edited by tlyons01; 05-01-2012 at 02:22 PM. Reason: spelling
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Old 05-01-2012, 04:17 PM
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Location: Lincolnton, NC
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Most people use 1 to 1.5 inches of soil and a 1.5-2 inch cap.

If you measure the length and width of your tank you can get the area, then put in the depth of soil you want and you can get a volume of soil.

I got the big bag of organic choice potting mix (32 quarts I believe) and I have about half the bag left over. After setting up my 40 gallon acrylic tank (which I think is actually more like a 37 gallon tank)

One big bag should be enough for a 46 gallon tank. But if you were concerned and didnt want to go back out to the store if you came up short you could get 2 bags. Then you will have extra for another tank or some other garden project.

As far as PFS goes, I can't really advise on how much you'd need b/c I capped with pea gravel. But the formula would work the same way. My guess would be 2 bags of sand.

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kamikazi is offline
Old 05-01-2012, 04:59 PM Thread Starter
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Thanks kamikazi. I already have the sand, it is what I am currently using. I wondered about the dirt, because I found a site that sells bags of soil at 3lbs per bag. I was trying to figure out how many bags I should be getting. They say on the site that 3 lbs is enough to set up a 10 gallon tank. What they do not say is how thick that makes the dirt. They could be referring to only 1/4 of an inch or more, there is no way to know, I guess. I would llike to use at least 1", but maybe as much as 1.5".
I will try your formula for volume and see if that works for me, I was always good at math IN GRADE SCHOOL!!!
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Old 05-01-2012, 11:13 PM
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Length x width x depth, all measured in the same units. For example, feet.

A tank that is 3' long, x 1' wide with 2" of substrate (mumble... mumble... 2" = .17 of a foot) = .5 cubic feet of material.

Now, convert gallons to cubic feet...
There are 7.5 gallons per cubic foot, so half a cubic foot = 3.75 gallons.
You can multiply that by 4 to get quarts (potting soil is often labeled in quarts): 3.75 x 4 = 15 quarts.

Sand and gravel weigh pretty close to 100 lbs per cubic foot, so if you are using sand or gravel you would need about 50 lbs.
Diana is offline
Old 05-02-2012, 06:51 AM
Planted Member

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Location: Villa Rica, GA
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There is a pretty sweet calculator built right in here at TPT, could use a few more options like AS though:

https://www.plantedtank.net/substratecalculator.html
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Old 05-02-2012, 02:20 PM
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Join Date: Jan 2010
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Liters are so close to quarts that you can use the formulas that give you the answer in quarts to see how many liters to buy. Or simply measure everything in centimeters. 1000 cubic centimeters = 1 liter.
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