# Flourite calculation error in seachems website



## netblues (Jan 26, 2005)

Hi everyone..
I was looking at seachems website trying to figure out how much flourite or onyx sand I need for a new planted 180L 100x50x40cm 
http://www.seachem.com/products/product_pages/Flourite.html
quoting >>This bag is sufficient for about a 5 cm (2 inch) deep bed in a typical 40 L (10 gallon) tank.

i.e. 7 kgs (one bag) is good for 40 L (10 gallons) which is about 200cm2 bottom area...
and then it goes on >>Recommended use is 1 kg (2 lbs) for approximately each 200 cm2 (31 in2) of tank bottom at a depth of 5 cm (2 in)...

So I either need three 7kg bags OR one bag is more than enough..
Which one is correct?

p.s Same happens in flourite red and onyx sand.


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## Laith (Sep 4, 2004)

Here's what I see on the Seachem site:

"This bag is sufficient for about a 5 cm (2 inch) deep bed in a typical 40 L (10 gallon) tank. Recommended use is 1 kg (2 lbs) for approximately each 200 cm2 (31 in2) of tank bottom at a depth of 5 cm (2 in)."

I'm not sure how you get 200cm2 for a 40l tank? 200cm2 is like 12cm x 16.6cm and a 20cm x 20cm x 20cm tank is only 8 liters with a tank bottom of 400cm2...

Or is my math wrong?


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## netblues (Jan 26, 2005)

Laith said:


> I'm not sure how you get 200cm2 for a 40l tank? 200cm2 is like 12cm x 16.6cm and a 20cm x 20cm x 20cm tank is only 8 liters with a tank bottom of 400cm2...
> 
> Or is my math wrong?


Well a 0,2m (=20cm) X 0,2m tank =0,04m2 or 40cm2 not 400cm2...bottom area

Think 1meter long tank widh 50cm depth IS 500cm2 and holds about 200liters...
200cm2 for 40 l is exagarating 130cm2 is more appropriate.. but makes the inital argument even worse.. (if we need one bag for 130cm2) this means 7kg/130cm2
while seachem says 1kgr/200cm2

Sorry to say your math is wrong.. ;-)


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## dennis (Mar 1, 2004)

A 10 gallon tank is 20 inches x 10 inches so its bottom area is 200" squared. I think there is a typo from seachem and the 200cm squared should have read 200 inches squared. Further, a 10 gallon tank is 50cm x 25cm (there are 2.5cm in an inch) or 1250cm squared. I know 1 bag of flourite is adequate for a tank of this size. If a bag is 7kg then 1250/7=178cm squared of coverage for each kg used. Seachem is telling you you need 1kg for every 200cmsquared. The difference of 12cm squared is negligable.

BTW a 1mx50cm tank would have a surface area of...100x50=5000cm squared. Sorry but your math *is* wrong. Further, you cannot say how many liters that example holds as there is no tank height given. If the tank were 1mx50cmx50cm it would have a volume of 250000cm cubed or 250liters (approx 66gallons)

HTH


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## netblues (Jan 26, 2005)

I was thinking in meters and forgot to mulitply for square. You are right.
This answers my question.. So I need 3 7kg bags...more or less..


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## dennis (Mar 1, 2004)

This is even easier though

http://www.plantedtank.net/substratecalculator.html

to convert cm to inches, divide the cm by 2.5 To conver kg to lbs, multiply kg by 2.2.

Actually for your 100x50cm tank you would need 83lbs/38kg for a 3" deep bed. I would highly recommend you use 3" of substrate and you can have it deep in the back of the tank. Generally you should use 1.5-2" in the very front and slope it back to about 3"+ in the back, 4" is ok to.


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## MatPat (Mar 22, 2004)

Dennis,

Leave it to a number crunching woodworker to work this one out  I though you said math wasn't your strong suit? I guess you worked with metrics in your shop too huh?


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## dennis (Mar 1, 2004)

Actually no, they have no idea what a cm is. I only learned it since I started in the hobby and only in the past few months has it really started sticking in my brain.

How much was in metric in your shop? Actually PM me so we don't steal this thread


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