Calculating water displacement of rock

[Sir Kon Salty Sox]

I promise I already searched forums, couldn't find answer. I am currently calculating how much stump remover to dump in my tank. Yikes.

I need a formula/calculator to compute the amount of water displaced by 130 pounds of live rock. I know that a "5 pound rock" is a relative idea, if you want to account for the amount of holes, but is there a ratio comparing lbs:displaced water that I could easily plug values into?

 

[T-J]

Simple answer: No.
You need to know how much water you put in your tank after aqua-scaping and filling it.
Like you said, it's all relative. Weight has no bearing on displacement.
Also, this thread may help:

Question about Spectracide Stump Remover dosing

I've seen a few threads on this topic in concerns to raising Nitrates. I picked up a bottle but haven't the slightest clue on how much to dose. Im not the best with math so the few calculations I have seen provided online don't allow me to come to my own conclusion.. afraid it will be off. So...

www.reef2reef.com

 

[Sir Kon Salty Sox]

I got on and used the excel spreadsheet calculator, and was "stumped" (pun intended) when I had to enter water volume in gallons. I think I will use above thread and an estimated value of 100g of water and proceed with my nerdy calculations.

I was starting to draw the rock and find the area under the curve using a bit of calculus but then remembered I got out of teaching math cause my students always said it had no real life applications

 

[jdpiii3]

use this calculator.

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[Sir Kon Salty Sox]

yes! thank you! I definitely calculated wrong, there is about 76 gallon according to this calcultor. i did not even thinka bout including substrate's displacement. dope!

 

[melonheadorion]

yes! thank you! I definitely calculated wrong, there is about 76 gallon according to this calcultor. i did not even thinka bout including substrate's displacement. dope!

when using these calculators, you have to remember a couple things. more specifically to rock. the weight of rock doesnt mean a whole lot. if you have a 5 pound rock that has the diameter of a basketball, and a 10 pound rock that has the diameter of a baseball, which of the two displaces more water

 

[Sir Kon Salty Sox]

when using these calculators, you have to remember a couple things. more specifically to rock. the weight of rock doesnt mean a whole lot. if you have a 5 pound rock that has the diameter of a basketball, and a 10 pound rock that has the diameter of a baseball, which of the two displaces more water

just when I started feeling confident in my calculations....

i am now even second guessing whether or not my nitrate is really 0. only used api test kits, and have read multiple places that nitrate just "doesn't disappear" it's just weird that the api was showing nitrate when cycling and none ever since

 

[jdpiii3]

when using these calculators, you have to remember a couple things. more specifically to rock. the weight of rock doesnt mean a whole lot. if you have a 5 pound rock that has the diameter of a basketball, and a 10 pound rock that has the diameter of a baseball, which of the two displaces more water

What weighs more 100 lb of rock or 100 lb of feathers.

10 lb is still going to displace 10 lb of water 5 lb will displaced 5 lb of water.

 

[T-J]

What weighs more 100 lb of rock or 100 lb of feathers.

10 lb is still going to displace 10 lb of water 5 lb will displaced 5 lb of water.

Wrong.
Water displacement is due to VOLUME of an object, not its weight.
A 5lb rock the size of a baseball will displace less water than a 2oz balloon inflated to the size of a basketball.

 

[Sir Kon Salty Sox]

A 5lb rock the size of a baseball will displace less water than a 2oz balloon inflated to the size of a basketball.

now there is a brilliant explanation. if I weren’t so lazy, I would just empty the tank and fill it back up after measuring the water.

I think however I will just be extremely forgiving in my calculations and start off as if there were say, 60 gallons of water and then slowly adjust

 

[melonheadorion]

What weighs more 100 lb of rock or 100 lb of feathers.

10 lb is still going to displace 10 lb of water 5 lb will displaced 5 lb of water.

only if it were weight that causes displacement. weight has literally, no effect on displacement at all. as mentioned by T-J, a basketball filled with air will displace more water if submerge it, more than a 20 pound weight lifting plate. the determining factor will be what space it takes up within the water, that determines displacement.
its easier to think of it as using measuring scale weights. they are usually small, brass, and have a predefined weight to them. submerging one of those comparable to something the same weight, but in a larger form, the item with a larger form will displace more water

 

[jdpiii3]

Wrong.
Water displacement is due to VOLUME of an object, not its weight.
A 5lb rock the size of a baseball will displace less water than a 2oz balloon inflated to the size of a basketball.

I guess my mom was right I should have paid more attention to my studies and less attention to playing sports I could have been a doctor.

Thanks for this simple explanation.

 

[Miami Reef]

Why can’t you plug in your tank with a lesser volume and do a before and after test to see the rise? If you know how much stump remover/gallon to raise a level of nitrate, you should easily be able to calculate the gallons of your tank.

Using a higher purity nitrate additives with a known concentration will be more accurate in determining tank gallon capacity.

This works well for nitrate since it doesn’t absorb into calcium based substrates. Phosphates would not be an ideal way to measure your tank gallon because your tank will appear to have more gallons since you will need to add more to achieve the same result.

 

[melonheadorion]

im on my second tank, so i learned my lesson when it came to things that needed to know water volume. my current tank, i measured the amount of water i put in after rocks were in, so it made it easier on myself to know actual water volume

 

[chinkle]

I promise I already searched forums, couldn't find answer. I am currently calculating how much stump remover to dump in my tank. Yikes.

I need a formula/calculator to compute the amount of water displaced by 130 pounds of live rock. I know that a "5 pound rock" is a relative idea, if you want to account for the amount of holes, but is there a ratio comparing lbs:displaced water that I could easily plug values into?

....so I have been thinking about that also...

 

[Randy Holmes-Farley]

I don’t think there’s any calculation of water displacement that is much more useful than an eyeball estimate.

There also isn’t a single exact answer. Is water in a pore that exchanges with the bulk water once per minute usefully included? Yes.

what about once per hour? Day? Week? Month?

 

[killer2001]

Could you find volume by measuring salinity if you have an accurate salinity measuring device? Lets say I have a 45 gallon tank, but with the rock and sand I know its less than 45 gallons. So if my salinity reads 35.55 ppt for example, then I add 1 gallon of RODI, and it becomes 35.45 ppt, is there an equation that can take that change of reference to find actual volume?

 

[Sir Kon Salty Sox]

To be honest, at this point, I’ve been eyeballing the stump remover powder (sooo little) and mixing it with some tank water in red solo cup, then squirting in 3-10 mL when corals look hungry. Tank has never looked better

 

[Randy Holmes-Farley]

Could you find volume by measuring salinity if you have an accurate salinity measuring device? Lets say I have a 45 gallon tank, but with the rock and sand I know its less than 45 gallons. So if my salinity reads 35.55 ppt for example, then I add 1 gallon of RODI, and it becomes 35.45 ppt, is there an equation that can take that change of reference to find actual volume?

Certainly one can do experiments like that. It will change over a period of time (rising as salt comes out of pores) and you’d need to control for evaporation.

 

[mermaid_life]

....so I have been thinking about that also...

This only applies to something that stays bouyant.