Water volume
- Thread starter Dutch_Roots
- Start date
I usually just subtract 20-25% from the vendor’s advertised volume (which may not be accurate) to get approximate net water volume. Agree with Jose, useful to know “accurate” volume for dosing but very challenging to account for water in overflow box, pipes, sump, etc. To me - close enough is more than enough. 
I think it's different for each system based on displacement. I just multiply the three dimensions and divide by 231, that's your total volume. Rock and sand will actually absorb water, especially dry rock and sand, but depending on the size of each rock, I probably deduct 15-20%? I think there's a lot less displacement these days with all of the negative space setups people use compared to the rock wall of the late 80's and 90's.
Quick and dirty ….Fill tank to 3/4 full with salt water (or RO water if you start with dry rocks and sand) . Make a mark on your tank at water level. Now put in sand and all the rocks you are thinking of putting in ( Don’t have to arrange the rocks … make sure no trap air pockets) The new water mark is your rock/sand ‘volume’.
Use the (lxwxh)/231 to find the volume of rock/sand.
Use the (lxwxh)/231 to find the volume of rock/sand.
Don't know if this helps
Displacement by Rock Type
Based on the average densities of common stone materials, a 5 lb rock's displacement varies as follows:
Displacement by Rock Type
Based on the average densities of common stone materials, a 5 lb rock's displacement varies as follows:
- Basalt (Dense): Displaces approx. 0.20 gallons (0.76 liters). Basalt is a heavy volcanic rock with a high density (
). - Granite (Common): Displaces approx. 0.22 gallons (0.83 liters). Granite is a standard reference for "hard rock" density (
). - Sandstone (Porous): Displaces approx. 0.25 gallons (0.95 liters). Sandstone is less dense (
) and often has higher porosity. - Live Rock (Aquarium): Displaces approx. 0.35 to 0.45 gallons (1.3 to 1.7 liters). These rocks are extremely porous; as a general rule of thumb, it takes about 1.75 kg (roughly 3.8 lbs) to displace 1 liter of water.
Well, after applying advanced reef fluid dynamics and displacement modeling, the net water volume of a reef aquarium can be approximated as:
V_net = ∭(Ω_wet) [1 − (ρ_rock + ρ_sand + ρ_equipment)] dV
− ΣV_plumbing
+ ∫(Q_RODI dt)
− ε_hanna
+ λ_reefkeeper
Where:
Ω_wet = the three-dimensional region actually containing water
ρ_rock = displacement density of “just a few pieces of live rock”
ρ_sand = displacement coefficient of the sand bed you promised would stay shallow
ρ_equipment = combined displacement factor of pumps, heaters, probes, frag racks,
magnetic cleaners, random clips, and mystery objects in the sump
ΣV_plumbing = cumulative water trapped in pipes, UV sterilizers, reactors, and fittings behind the stand
∫(Q_RODI dt) = total volume added during the initial fill (adjusted for membrane efficiency and snack breaks)
ε_hanna = alkalinity testing error after the second retest
λ_reefkeeper = hobbyist optimism correction factor
Boundary conditions:
Alk must be stable, ORP must be confusingly high,
and the reefer must have already ordered more coral.
OR: I would just go with 75-80% of manufacturer’s advertised volume.
However, I typically just round up to the nearest 100gal so I can be better than my neighbor Bob! lol
V_net = ∭(Ω_wet) [1 − (ρ_rock + ρ_sand + ρ_equipment)] dV
− ΣV_plumbing
+ ∫(Q_RODI dt)
− ε_hanna
+ λ_reefkeeper
Where:
Ω_wet = the three-dimensional region actually containing water
ρ_rock = displacement density of “just a few pieces of live rock”
ρ_sand = displacement coefficient of the sand bed you promised would stay shallow
ρ_equipment = combined displacement factor of pumps, heaters, probes, frag racks,
magnetic cleaners, random clips, and mystery objects in the sump
ΣV_plumbing = cumulative water trapped in pipes, UV sterilizers, reactors, and fittings behind the stand
∫(Q_RODI dt) = total volume added during the initial fill (adjusted for membrane efficiency and snack breaks)
ε_hanna = alkalinity testing error after the second retest
λ_reefkeeper = hobbyist optimism correction factor
Boundary conditions:
Alk must be stable, ORP must be confusingly high,
and the reefer must have already ordered more coral.
OR: I would just go with 75-80% of manufacturer’s advertised volume.
However, I typically just round up to the nearest 100gal so I can be better than my neighbor Bob! lol
Well, after applying advanced reef fluid dynamics and displacement modeling, the net water volume of a reef aquarium can be approximated as:
V_net = ∭(Ω_wet) [1 − (ρ_rock + ρ_sand + ρ_equipment)] dV
− ΣV_plumbing
+ ∫(Q_RODI dt)
− ε_hanna
+ λ_reefkeeper
Where:
Ω_wet = the three-dimensional region actually containing water
ρ_rock = displacement density of “just a few pieces of live rock”
ρ_sand = displacement coefficient of the sand bed you promised would stay shallow
ρ_equipment = combined displacement factor of pumps, heaters, probes, frag racks,
magnetic cleaners, random clips, and mystery objects in the sump
ΣV_plumbing = cumulative water trapped in pipes, UV sterilizers, reactors, and fittings behind the stand
∫(Q_RODI dt) = total volume added during the initial fill (adjusted for membrane efficiency and snack breaks)
ε_hanna = alkalinity testing error after the second retest
λ_reefkeeper = hobbyist optimism correction factor
Boundary conditions:
Alk must be stable, ORP must be confusingly high,
and the reefer must have already ordered more coral.
OR: I would just go with 75-80% of manufacturer’s advertised volume.
However, I typically just round up to the nearest 100gal so I can be better than my neighbor Bob! lol
V_net = ∭(Ω_wet) [1 − (ρ_rock + ρ_sand + ρ_equipment)] dV
− ΣV_plumbing
+ ∫(Q_RODI dt)
− ε_hanna
+ λ_reefkeeper
Where:
Ω_wet = the three-dimensional region actually containing water
ρ_rock = displacement density of “just a few pieces of live rock”
ρ_sand = displacement coefficient of the sand bed you promised would stay shallow
ρ_equipment = combined displacement factor of pumps, heaters, probes, frag racks,
magnetic cleaners, random clips, and mystery objects in the sump
ΣV_plumbing = cumulative water trapped in pipes, UV sterilizers, reactors, and fittings behind the stand
∫(Q_RODI dt) = total volume added during the initial fill (adjusted for membrane efficiency and snack breaks)
ε_hanna = alkalinity testing error after the second retest
λ_reefkeeper = hobbyist optimism correction factor
Boundary conditions:
Alk must be stable, ORP must be confusingly high,
and the reefer must have already ordered more coral.
OR: I would just go with 75-80% of manufacturer’s advertised volume.
However, I typically just round up to the nearest 100gal so I can be better than my neighbor Bob! lol
