water displacement by LR

[swishyfishies]

I'm curious of how much water is displaced from the original tank water capacity once the average porous LR is added.

Like my tank, it holds 55 gal of water....but say I add 55 lbs of Fiji or Mashal Islands LR how many gallons of water is actually left on my tank?

I know that's actually the amount I need to go by for my stocking level & amount of water to be changed out.

 

[reefrunner69]

Depending on how much rock you have, I'd guess you displace 10-20% of the tank volume. FWIW, I use the gross volume for stocking purposes and the net volume for waterchanges.

 

[mulron]

here's my 2 cents.

Next time you do a water change you could take a piece of LR out let it drain a minute. Weight that piece on a scale. Empty about half of a 5gal bucket into the tank. Mark the water level on the bucket and then put the rock in. Mark that level on the bucket. At this point remove the LR and let it drain a min. Place back in your tank. Then using a measuring cup, you can take water from the tank and just keep pouring until you reach the new line.

example: takes 2 cups of water for 1 lb of rock.

so 55 lbs of rock displaces 110cups of water. there are 16 cups in a gal, so the example would displace 6.8gals of water.

Of course fiji and Marshall LR have different densitys. So you would have to do this 2 times.


/shrug that would get you in the ballpark, or just assume what Kevin said above will probably save you time.

 

[reefrunner69]

/shrug that would get you in the ballpark, or just assume what Kevin said above will probably save you time.

Actually that's a pretty good idea, and what Kevin said above was guess.

Another way to figure it (since I know you don't have the rock yet) would be to have a known amount of water in your tank say 30g, add the rock, to fill the tank (55g), took an additional 10g, the difference of 15g is how much water was displaced by your rock.....

 

[Guest]

Ok, that is a hard math problem. It has to do with mass.

My way of thinking is if your rock is approximately the size of a gallon jug of water, I would say you would displace a gallon of water. You can size down as you would like...This of course doesn't count the density and the ability to absorb water.

The mass of the object will determine how much water is displaced. Since rocks are all different sizes, you can try to visualize how many of your rocks it would take to fill a gallon jug and then think of gallons. give or take a few ounces for gaps. Or , you cando what the others above say.

 

[swishyfishies]

reefrunner, I like your idea the best. I'll make sure I do that when I get my stuff going.

 

[Hara]

man, you guys are too scientific for me...I just take out 4 buckets full and call it good

 

[mulron]

yea if you have not setup the tank yet, then by all means go with reefrunner's plan. It would be easiest and pretty accurate.

have fun