Determining The Water Volume Of Your Whole Reef System

And that's the EXACT same answer I got one week ago (Matt thought it was wrong and nobody else even acknowledged the answer). Is there a reason almost EVERYBODY keeps ignoring this fact? Am I the red-headed step child?

 

I just haven't been up to doing the math. This whole thing with arguing over the answer got me motivated. Along with being a bit bored.

 

You used the exact same formula, just worded differently. Now that 2 people have the same answer, maybe we can get some interaction with "others".

 

If Matt had filled his tank with a 2 gallon bucket and used 15 of them to fill the system
he would have 30 gallons in there

The formula is sound
it worked on my 78 gallon

Steve

 

Wow. This got interesting! If you guys are right that is a lot less water than I thought. I have removed 10 gallons just from my sump and it seemed like there were at least 4 gallons left in there. I have a refugium which holds a couple gallons, maybe as much as 4. And as stated, my tank is 36 gallons. I do have a bunch of rock in there, but it would still be a big surprise to have only 30 gallons overall. Reeron do you have red hair?

matt

 

Reefsparky,

If you want to eliminate the 3% error in your revised calculation, here's a thought.

Let's say you estimate 100 gallons initially and based on your method, the new estimate comes out 105 or whatever. Your new estimate is 105.

Mark the current water level in your pump section of your sump. Turn off your ATO and let water evaporate out of your pump section of your sump. After an inch has evaporated out, it is easy to estimate just the evaporated volume... length x width x depth of evaporated volume of the pump section. Let's call that "evaporate". Arbitrarily for this example, let's say evaporate is 4 gallons. Thus, your third estimate would be 105 gallons (previous new estimate) minus the evaporate (4 gallons). This equals 101 gallons.

Then recursively repeat your previous procedure. Each time you repeat the exercise, you should zero in on the final answer.

Just a thought.

Mark

 

Ok, so I just did this for my tank tonight. I have the 65g RSM, with a sump filled to approx. 12g. I used my Pinpoint Salinity meter to measure, and used their conversion charts on the website to convert from mS to SG.

I realized SG is a requirement with my equation, or it doesn't work, since you don't want to use 0 at any point during the multiplication. I'm guessing this is a big factor in why SG is still a popular unit for science involving saltwater.

Tank was at 1.0241sg. I added 2.5g RODI to top off (1 sg). I waited 1/2 hour after that, and got a reading of 1.0231sg.

After plugging in and letting the calculator do the work, I got 60.78 gallons. That sound like it's about accurate for my system. I consider it right, because my tank's alk and calcium additions have always been about 35% off from where they should be; the levels raise by 35% more than they should have. I dosed on the assumption of 65g, while I had 45g.

BTW, you can figure out your tank's volume by dosing alk, mag or calcium, if you can measure the amount you're dosing, and its concentration, accurately enough. Magnesium would likely be easiest, as it's usually the highest in volume at a dose. Alk would be hardest, since it's usually measured in mL vs the ounces of mag, or gallons of topoff. A one drop difference throws the calculation off by more with alk.

 

measuring metals

@BlackRaven---
"BTW, you can figure out your tank's volume by dosing alk, mag or calcium, if you can measure the amount you're dosing, and its concentration, accurately enough. Magnesium would likely be easiest, as it's usually the highest in volume at a dose. Alk would be hardest, since it's usually measured in mL vs the ounces of mag, or gallons of topoff. A one drop difference throws the calculation off by more with alk."
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Yes, I believe you can. You can try this:

(1) Measure your Calcium concentration of your tank.

(2) Get some Calcium chloride solution(CaCl2) by seachem or Kent or anyone. I think it comes in 100,000 ppm Ca. (If it is CaCl2

at 100,000 ppm, I will do the stoichiometry for you if needed (since Ca is 40.08 g/mol and Cl is 35.45 g/mol)

(3) add 20 ml (V1) of 100,000 ppm Ca (C1) to your total volume tank setup (V2).

(4) measure the new calcium level (C2) after the add. (C2< C1) you will need to use the difference in Ca of course, like 400

before and 425 after, would make C2 (Cf-Ci) or 25 ppm

(5) Here we would solve for V2: C1*V1=C2*V2 or V2= (C1*V1/C2) or (20ml * 100,000ppm)/25ppm = 80,000 ml= 21 gallons

If C2 tested at only 10ppm diff, that would mean V2 would be (20ml x 100,000ppm)/10ppm = 200,000ml= 52 gallons or so of water.

One problem here is the accuracy of the measurements, and true concentration of Ca additive. I used to use an ICP-ES and an AA

to test for trace metals, and did serial dilutions to measure for major components like Sr, Mg and Ca.

 

Just tried this. I am having a hard time believing the answer.

To review I have a 36 gallon display tank, 18x18x18 sump with 10 inches of water and a refugium that I estimate could be 3 - 4 gallons with just water...

My SG at start: 36.3 (1.027)
I added 32 ounces of ro water.

SG was just over 1.026 after 20 minutes or so.

I did the math... got 6.73 total gallons.

Obviously that is wrong.

So I figured I didn't add enough water - so I added 32 more ounces.

Waited 15 minutes or so, SG was just under 1.026.

This time, if I take the just over 1.026 initial reading (before the 2nd addition of 32 ounces) as the initial SG and use the just under 1.026 as the resultant SG, then I get a number close to 30 gallons (29.08 ) which is damn close to what you guys were guessing my total water volume to be (30 gallons)...

but the whole exercise did not give me confidence. I still don't really know what my total water volume is.

matt

 

I'm just wondering, Matt, what resolution can you read your SG to? Do you have a digit past 1.026? Also, how much rock do you have in the tank, pound-wise, and does it happen to be marcorocks or reefcleaners? If it is, it's about the same density as mine, so I can ballpark the loss due to its volume.