OK, now my brain hurts . . .

[Rockcrawler]

So, I am sitting in front of my tank last night.
Just watching life pass by.

I have a 75 gal + 20 gal sump = 95 gal system.

I have 145# of LR, so 1.933 lbs/gallon in the tank.

Now I know that water weighs 8.34#/gal fresh and 8.6#/gal for saltwater (depending on temperture, etc. but this is close enough for us).

I know the weight of the rock but the density varies so I cannot calculate how many gallons are taken up by the LR.

SO now I guess I gotta unload a few big chunks and check how much space it takes up so that I can calculate the density SO I can estimate exactly how many gallons of water I have in the system. NOT 95 but How Many? One has to know!

Also I am wondering why I thought about this in the first place.

?????????

My head hurts . . .

8O

 

[dianeww]

Also I am wondering why I thought about this in the first place.

Not that critical!! Why does one have to know?

 

[Fireworks]

After loading my dry tank with rock, I measured how much water it took to fill. I wanted to see how much water the rock displaced. This only works the first time you set up.

 

[Rockcrawler]

Well the reason I was wondering is -

Everything you add to the water is based on how many gallons you are adding it to.
If you add chemicals to raise calc or alk or whatever you add for how many gallons.
With a large quantity of LR (I have 145 lbs of LR in a 75+20=95 gallon system) The rock displaces water to a large extent.

I am going to try weighing some of my rock to get at least an estimation of how many gallons I have lost.

I am thinking I have lost in the neighborhood of 35-40 gallons of water capacity, that has been displaced by LR. That can have a significate impact on dosing.

I am dosing a 60 gallon system instead of 95 gallons.

What do y'all think ????

 

[runway1]

Well, first, the water displacement is a function of the rock's volume not its density. Weighing the rock will get you nowhere.

Fireworks has the best solution. If you MUST know then:
1. fill a container large enough to hold all the rock in question to the very top edge.
2. Have a catch basin underneath to catch ALL the overflow.
3. Slowly place the rock into the container - the displacement will cause the water to spill.
4. After the rock has been submerged, measure the resulting spill. This will be the exact volume of the rock introduced and therefore the precise water volume displaced.

Seems like a lot of work for negligible info. You could probably "eyeball" the approximate volumetric displacement and come within 10%-20% of actual.

 

[hcuellart]

I'd treat/supplement for 75 gallons

 

[BillyZ]

I wouldn't worry about getting that exact.

the easiest way to measure how much your substrate it taking up, 231 cubic inches in a gallon. measure width, length and dept and subract your substrate volume from total volume.

If your tank has been set up for a while, and has fish etc in it, I wouldn't disturb the LR unnessisarily for this. Just ball park it. You shouldn't be adjusting any water parameters that drastically anyway, so being off by 5 or 10 gallons when determining how much to dose, shouldn't be an issue.