Estimating tank water volume (unknown amount of live rock)

Meatball_reef · Jan 25, 2019

I'm trying to get a good idea of what my water volume is. I've had the rock for a long time and do not remember how much is actually in there. I've got a sump below, and I think I can get a decent idea of whats in there, but I'm lost as to how to estimate how much volume the rock is taking up.

Right now my logic is - I could fit the amount of rock that's already in there maybe 2 more times to fill the tank. So, if the tank is a 40 gal breeder, I'm thinking the rock takes up ~13.333 gallons.

Is this a good way to estimate? Thoughts?

James M · Jan 25, 2019

Well there’s different sizes of rock ....very hard to tell without knowing how much ponds of rock for sure

Rakie · Jan 25, 2019

So you didn't ask -- You will need at least one more light like that, and you should probably raise it 4-5" more, it'll help.

Otherwise most people assume rockwork takes between 25-33% of water volume. And sump typically only gives you about 25% of ITS water volume.

So a standard 40g with a 40g sump, could potentially be 40 gallons when you subtract rockwork and sand, then add the bit you get from sump (which is typically less than half full, then equipment takes about 15%+ of the remainder).

lapin · Jan 25, 2019

Just looking with my glasses on, I see said the blind man.
40 gallon breeder = prob 38 to 36 gallons full, depending on overflow type. Rock takes up 5 gallons depending on how porous. Sand maybe a gallon.

Meatball_reef · Jan 25, 2019

Rakie, appreciate the thoughts on the light. Was planning on getting another at some point down the line but didn't think about raising it.

The sump is a 20 long. Maybe 1/2 full, with a protein skimmer and pump, and a large return pump.

Lapin - rock takes up 5 gallons. Do you mean one rock?

Thanks all.

Rakie · Jan 25, 2019

I think that the rockwork you have must be taking up at least 10 gallons space in my opinion, but that's just me.

Meatball_reef · Jan 25, 2019

Appreciate the opinion, I wanted to get some other eyes on the tank.

lapin · Jan 25, 2019

I mean its hard to tell but at least 5 gallons could be 10 could be 15

Rakie · Jan 25, 2019

Meatball_reef said:
Appreciate the opinion, I wanted to get some other eyes on the tank.

The truth is we can't accurately answer these questions if you can't accurately answer ours.

What kind a rock? how many pounds? etc etc.

Were booth shooting blind trying to hit a barn in the dark haha

mshonk · Jan 30, 2019

Rakie said:
So you didn't ask -- You will need at least one more light like that, and you should probably raise it 4-5" more, it'll help.

Otherwise most people assume rockwork takes between 25-33% of water volume. And sump typically only gives you about 25% of ITS water volume.

So a standard 40g with a 40g sump, could potentially be 40 gallons when you subtract rockwork and sand, then add the bit you get from sump (which is typically less than half full, then equipment takes about 15%+ of the remainder).

I don think one more light is necessary varying on what you would like to keep. I have what seems to be the same light ove a 40g breeder and I keep sps on the bottom 6" from the edge of the tank. In fact I have over 30 pieces of sps in mine. I run the lights at 100/100 though. Sps high in the tank see upwards of 600 PAR the ones at the bottom see 350+. As for volume I am following along I know my approximate lbs but not 100 percent.

mshonk · Jan 30, 2019

If you want a precise measurement I would start with the easy part, the sump. A cubic foot holds 7.481. For example the first chamber of my sump is 10.25" x 11" x 12" = .783 ft³. So .783 x 7.7481 = 5.857623g in that chamber etc.

You don't look like you have a lot of livestock glued to the rocks, I would grab some containers, kill the pumps, let all of the water settle, fill the containers with the rocks letting them drain the best you can, level the sand, take and record all of your measurements[ dt and sump, also the dimensions of the space occupied by the sand to get a ballpark], put the rock back and do the math. other than that it is all speculation.