System Water Volume Calculation?

[SPR]

I am just trying to get a more accurate guess of my system water volume in my Max S 650 for dosing calculations etc. The system I believe holds 650 litres and specs as per Red Sea web site

When I built it I think I roughly added 573 litres of water (with around 70kg Rock/20kg sand at the time already in) which I counted when adding. This is a rough guide

I now have approx:
80kg live rock
20kg sand

That's about it apart from fish/coral volume and the corals are not that big yet.

So for the mathematicians out there what's the actual water volume in the system??

PS. My maths is not good which is why I ask!

 

[DaveK]

To compute the volume of water in an empty cube is easy. With the dimensions in inches, you multiply the length times the width times the depth and then divide by 231 to get the volume in US gallons. For metric measurements in cm, you multiply the length times the width times the depth and then divide by 1000 to get the volume in liters.

However, this doesn't solve your problem, because you still need to account for all the rock and sand in the system. This part is impossible to do because each system is different.

The method you used of counting how much water you added is about as accurate as your going to get. As for dosing, that number is a good place to start. In any case, once you start dosing, you'll maintain the rate of dosing by doing water tests, and then making adjustments up or down. Every tank is going to be different here also, since everyone has different fish and corals in their system.

 

[SPR]

Thanks yes i understand that

But i think there must be a mathematical calculation to convert mass/kg into volume.unfortunately my maths isn't up to that part


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[DaveR11]

Unless you know the density of a material there is no way of relating mass and volume. A cubic meter of polystyrene will have a mass significantly less than a cubic meter of water and both will have a significantly lower mass than the same volume of lead. You could only approximate the densities of coral sand and rock and the rock, by the nature of the sort of stuff we want in our tanks, will be full of air holes.

Achimedes principle that a solid, when immersed in a liquid will displace its own volume of liquid, would be the best way to find out and you have effectively done that. You know the maximum volume of your tank, you have put rocks and sand in and you measured the actual amount of water you added - the difference is volume of the rocks and sand. I know that doesn't help you now that you have added more rocks but if you really want to be precise take out only the extra rocks you added - put them in a bucket of salt water at say a water change time and see how much water they displace. Then subtract these figures from the total volume of water you added when you set the tank up. This still won't account for fish, inverts etc but how accurate do you want?

 

[SPR]

Unless you know the density of a material there is no way of relating mass and volume. A cubic meter of polystyrene will have a mass significantly less than a cubic meter of water and both will have a significantly lower mass than the same volume of lead. You could only approximate the densities of coral sand and rock and the rock, by the nature of the sort of stuff we want in our tanks, will be full of air holes.

Achimedes principle that a solid, when immersed in a liquid will displace its own volume of liquid, would be the best way to find out and you have effectively done that. You know the maximum volume of your tank, you have put rocks and sand in and you measured the actual amount of water you added - the difference is volume of the rocks and sand. I know that doesn't help you now that you have added more rocks but if you really want to be precise take out only the extra rocks you added - put them in a bucket of salt water at say a water change time and see how much water they displace. Then subtract these figures from the total volume of water you added when you set the tank up. This still won't account for fish, inverts etc but how accurate do you want?

Mmm. Think i best stick with my estimate then!

I originally counted 573 litres

As a matter of interest DaveR11 what figure to you use as we have same tank obviously different rocks etc??


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[DaveR11]

Mmm. Think i best stick with my estimate then!

I originally counted 573 litres

As a matter of interest DaveR11 what figure to you use as we have same tank obviously different rocks etc??


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I reckon on 550 litres for mine

 

[SPR]

Yes i was going to go for about 550-560 after adding some more rocks so about the same


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[Tariq]

You could just take 1 piece of rock, weight it, carry out a archimedes test to get volume of water for a single piece then use that to estimate the density of remaining rock. You could also do the same for a measured amount of sand although it would have to be dry'ish (as it comes wet in the bag) so not as accurate.
Probably stick with estimate.


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