Interesting Read
- Thread starter celaeno
- Start date
5teady_2012
Here to help
I thought most people knew this anyways?
Ace Of Spades
Fish Gatherer
Me 2, Gravel, decor etc....Bet most peoples Mbuna tanks only hold around 60% of the water considering how much rock is inside
It's not always about the amount of water, but the dimensions!!
tangokitty
Fish Addict
So a bare bottom 55 gallon only hold 45 gallons?
blodhi74
Fishaholic
good post
Ficious
Fish Addict
this article is pointless...for one, yes...anyone with common sense know this.
my second point
from the article-
"You might not think it's important to know the specifics, especially if you're running a lightly stocked tank"...
..."It can mean the difference between having a tank that's healthy & easy to care for and having a tank where, despite your best efforts, your fish and other pets have to struggle to survive."
people dont usualy say, "oh this 20 gallon isnt going to really be 20 gallons so ill buy fish considering its a 15.4 gallon"
my 36 gallon is a bit overstocked, but since its already the way it is (30.4 gallons) it makes no difference.
its hard to say what im trying to say...but im sure fish people would love to theorize about this subject...consider this plus the surface area of a tank...now with that, prove how many fish would fit happily.
theyre theories until someone proves them
this article is pointless...for one, yes...anyone with common sense know this.
my second point
from the article-
"You might not think it's important to know the specifics, especially if you're running a lightly stocked tank"...
..."It can mean the difference between having a tank that's healthy & easy to care for and having a tank where, despite your best efforts, your fish and other pets have to struggle to survive."
people dont usualy say, "oh this 20 gallon isnt going to really be 20 gallons so ill buy fish considering its a 15.4 gallon"
my 36 gallon is a bit overstocked, but since its already the way it is (30.4 gallons) it makes no difference.
its hard to say what im trying to say...but im sure fish people would love to theorize about this subject...consider this plus the surface area of a tank...now with that, prove how many fish would fit happily.
theyre theories until someone proves them
my second point
from the article-
"You might not think it's important to know the specifics, especially if you're running a lightly stocked tank"...
..."It can mean the difference between having a tank that's healthy & easy to care for and having a tank where, despite your best efforts, your fish and other pets have to struggle to survive."
people dont usualy say, "oh this 20 gallon isnt going to really be 20 gallons so ill buy fish considering its a 15.4 gallon"
my 36 gallon is a bit overstocked, but since its already the way it is (30.4 gallons) it makes no difference.
its hard to say what im trying to say...but im sure fish people would love to theorize about this subject...consider this plus the surface area of a tank...now with that, prove how many fish would fit happily.
theyre theories until someone proves them
this article is pointless...for one, yes...anyone with common sense know this.
my second point
from the article-
"You might not think it's important to know the specifics, especially if you're running a lightly stocked tank"...
..."It can mean the difference between having a tank that's healthy & easy to care for and having a tank where, despite your best efforts, your fish and other pets have to struggle to survive."
people dont usualy say, "oh this 20 gallon isnt going to really be 20 gallons so ill buy fish considering its a 15.4 gallon"
my 36 gallon is a bit overstocked, but since its already the way it is (30.4 gallons) it makes no difference.
its hard to say what im trying to say...but im sure fish people would love to theorize about this subject...consider this plus the surface area of a tank...now with that, prove how many fish would fit happily.
theyre theories until someone proves them
I was interested in this article, as it's very useful to know the exact volume of water you've got for dosing medications etc., but I'd question some of the arithmetic. OK, you probably want to skip the rest of this post... 
Perhaps I need to get out more...
First of all, the author's calculation of internal volume of the tank versus the external volume may be true for a particular type of glass tank, but would not necessarily apply to all tanks. The internal volume of my acrylic tank to the water surface works out at about 71.4 litres, compared with its nominal volume of 75 litres (approx 20 US gallons). Subtract a bit for the slightly curved front corners, takes it to about 71 litres (being cautious) or about 19 US gallons, but on the other hand, I could fill it a bit deeper without flooding. This is rather different from the author's calculation of 16.5 - 17.5 gallons for a 20 gallon glass tank.
Secondly, I'm not convinced by the statements about displacement by the substrate, suggesting that you should calculate the volume of substrate by measuring its depth, width and height, and subtract that volume from the amount of water. This would only work for a complete solid, which displaced that volume of water - but most normal substrates are not packed solid - a certain amount of water finds its way into the spaces between the gravel or sand particles. If you put dry substrate into your tank, and then started pouring in water, you'd have to add a significant amount of water before it reached the surface of the substrate, especially if you were using large gravel or marbles.
I just did a quick experiment with some 3mm pea gravel scooped out of my aquarium into a jug. The calculated volume based on surface area times depth, as the article's author suggests, came to 50cc. I added water until it reached the surface of the gravel - this was about 20cc water (difficult to be precise as the surface was uneven). This is not a very accurate experiment - in an aquarium, the gravel would pack differently, and small variations in the surface height would be easier to allow for, but it suggests that maybe 40% of the volume of this substrate could be water, depending on how it was packed.
The author also suggests that you can calculate the volume of water displaced from the weight of your substrate and decor. I'd also dispute that - a couple of small lead plant weights can weigh as much as a large piece of plastic driftwood, but the weights will displace significantly less water. I'm struggling with the maths, as I'm not used to US gallons and pounds, but the author asserts that 'One pound of substrate displaces about .078 gallons of water volume'. Again, using my gravel, 3.6oz displaced about 30cc water (or 0.00792 US gal). If I've done the conversion correctly (and it's quite possible I've got this bit wrong - please be kind if so...), this means 1lb would displace 0.0352 US gallons, which is less than half the amount stated - now my gravel was wet, so would have been heavier than dry gravel, but even so, that seems like a large discrepancy. I would expect that sand would displace more water than the same depth of pea gravel, and large gravel, marbles etc. would displace less. As Ace says above, large rocks will each displace significant amounts of water as they are solid.
Short of emptying my tank, drying out the gravel, and adding measured volumes of water, I can't be more accurate than this, but I don't think the figures in this article are generally applicable or any more useful than the approximations that most of us currently use.
Now where did I leave my sense of proportion...?
Perhaps I need to get out more...First of all, the author's calculation of internal volume of the tank versus the external volume may be true for a particular type of glass tank, but would not necessarily apply to all tanks. The internal volume of my acrylic tank to the water surface works out at about 71.4 litres, compared with its nominal volume of 75 litres (approx 20 US gallons). Subtract a bit for the slightly curved front corners, takes it to about 71 litres (being cautious) or about 19 US gallons, but on the other hand, I could fill it a bit deeper without flooding. This is rather different from the author's calculation of 16.5 - 17.5 gallons for a 20 gallon glass tank.
Secondly, I'm not convinced by the statements about displacement by the substrate, suggesting that you should calculate the volume of substrate by measuring its depth, width and height, and subtract that volume from the amount of water. This would only work for a complete solid, which displaced that volume of water - but most normal substrates are not packed solid - a certain amount of water finds its way into the spaces between the gravel or sand particles. If you put dry substrate into your tank, and then started pouring in water, you'd have to add a significant amount of water before it reached the surface of the substrate, especially if you were using large gravel or marbles.
I just did a quick experiment with some 3mm pea gravel scooped out of my aquarium into a jug. The calculated volume based on surface area times depth, as the article's author suggests, came to 50cc. I added water until it reached the surface of the gravel - this was about 20cc water (difficult to be precise as the surface was uneven). This is not a very accurate experiment - in an aquarium, the gravel would pack differently, and small variations in the surface height would be easier to allow for, but it suggests that maybe 40% of the volume of this substrate could be water, depending on how it was packed.
The author also suggests that you can calculate the volume of water displaced from the weight of your substrate and decor. I'd also dispute that - a couple of small lead plant weights can weigh as much as a large piece of plastic driftwood, but the weights will displace significantly less water. I'm struggling with the maths, as I'm not used to US gallons and pounds, but the author asserts that 'One pound of substrate displaces about .078 gallons of water volume'. Again, using my gravel, 3.6oz displaced about 30cc water (or 0.00792 US gal). If I've done the conversion correctly (and it's quite possible I've got this bit wrong - please be kind if so...), this means 1lb would displace 0.0352 US gallons, which is less than half the amount stated - now my gravel was wet, so would have been heavier than dry gravel, but even so, that seems like a large discrepancy. I would expect that sand would displace more water than the same depth of pea gravel, and large gravel, marbles etc. would displace less. As Ace says above, large rocks will each displace significant amounts of water as they are solid.
Short of emptying my tank, drying out the gravel, and adding measured volumes of water, I can't be more accurate than this, but I don't think the figures in this article are generally applicable or any more useful than the approximations that most of us currently use.
Now where did I leave my sense of proportion...?
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