Calculating sand/rock displacement

[bmk]

Hi
What is the formula for calculating a tanks volume taking into account the displacement of sand/rock. My tank is 92cm x41cm x 55cm (180 Litres) with a 2" sand bed and approx 33kg of live rock.

Thanks
Barry

[toby16]

think maybe 150L

[bmk]

Hi
How did you calculate 150L

Barry

[S_Stoney_S]

It depends so much on the weight of the rocks, best way to do it was to measure how much water went in when you filled it up.

However you could just estimate the area that the rocks and the sand takes up in the tank. For example 100l tank. sand takes up 2% of the total volume. Rocks take up 40% of the volume. Therefore you actually have 58l of water in the tank. ROUGHLY. Of course your rocks and sand are porus, so its probably best to under estimate the volume the rocks and sand take up.