Determining The Water Volume Of Your Whole Reef System

So I've been working for some time on improving the above method. The method in the original article worked, but it was a bit awkward in execution. It requires the tester to make an estimate of what he/she thought the total system volume was. That was inconvenient.

I'd been trying to set up an equasion using a proportion. Deep down I knew that given the 3 known quantities (volume of RO/DI water added, SG of original tank water, and SG of tank water after addition of RO/DI water) it would be possible to calculate the "unknown" quantity, or total tank water volume.

Well, with the help of a knowledgable person on the Zeovit site, I found the missing link!

So here's the full equasion. Hard to find from scratch, but easy as heck to use!

V1 = (V0 x S2) / (S1-S2)

where,

V1 is the unknown quantity of your entire reef system, in gallons/ounces/ml.
V0 is the volume of RO/DI water added, in gallons/ounces/ml. (just use the same unit for the entire equasion).
S1 is the initial salinity, in SG, of your reef tank.
S2 is the resultant salinity.

As a test, I mixed up exactly 32 ounces of new saltwater with Coralife mix and RO/DI water, to a SG of 35 ppt. (1.026 on the refractometer). I then added exactly 8 ounces of RO/DI water and checked the SG again. It now fell dead between 1.020 (27.2 ppt.) and 1.021 (28.5 ppt.). Using the chart below, I took the average of the two and used 27.85 ppt.

So using the above equasion, here's how it came out.



V1 = (V0 x S2) / (S1-S2)

Total Volume = (8 oz. x 27.85 ppt) / (35 ppt. - 27.85 ppt.)

here it is without units:

Total Volume = (8 x 27.85) / (35 - 27.85)

Total Volume = 222.8 / 7.15

Total Volume = 31.16 oz.

So my "unknown" was actually 32 oz., but I calculated 31.06. That's a 2.6% discrepancy that I attribute to reading the refractometer. I can live with plus or minus 3%.

So, to sum it up--If you were reluctant to try to find the total volume of your entire reef system using the the original article--you now have no excuses. There's no complex math, no exasperating percentages. Just plug in the numbers in the equasion, and you're done.

Give it a try. Gone are the days when you weren't sure how much water you had. There's no concern with the amount of live rock, sand, the volume of your sump, skimmer, reactor, or water displaced by your 3 pound grouper! All you need is a refractometer, a bucket to measure/mix the water you add; and a calculator--and you can find out with a 3% degree of error, EXACTLY how many gallons your entire reef system has.

Here's a table of SG to Salinity ppt.




Specific Gravity to Salinity Conversions


Specific Gravity.....................................................Salinity, ppt.
1.015 ................................................................ 20.8
1.016................................................................. 22.0
1.017................................................................. 23.3
1.018 ................................................................ 24.6
1.019................................................................. 25.9
1.020................................................................. 27.2
1.021................................................................. 28.5
1.022................................................................. 29.8
1.023................................................................. 31.1
1.024................................................................. 32.4
1.025 ................................................................ 33.7
1.026................................................................. 35.0
1.027 ................................................................ 36.3
1.028................................................................. 37.6

 

Ok I am going to second ReefSparky for president.
This is fantastic.
I have made this a sticky.
I am anxious to try this out as I have been trying to calibrate my dosing lately.

matt

 

Wow, That's a lot to take in. haha...I shall read this over again & then try to figure out my water volume. Kudos!

 

The new formula is much easier. K+ to you.

 

Thanks, guys.

 

Related question, as you know I did a water water change to correct a mag flub today (went well by the way) anway, my SG from all my mad dosing lately floated up to 1.030. I made exactly 10 gallons of new water today at 1.018.
After the water change it mixed for a while and I pulled out the refractometer and tested again - it was exactly 1.026. (woohoo!)

Can you (or anybody else) tell me my total water volume from that?

matt

 

I'm going to say about 30 gallons.

 

clear this up?

You're doing this test with a small volume of water I don't see how it could work with a large volume. Lets say you test your aquarium sg before you top off, you get 1.027 that's 36.3 ppt. Now you add 64oz 1/2 gal, you wait take a reading you get 1.026 and 35ppt this equations get squirrely. It doesn't work. And if you add 8 oz to your 32oz your sg is from 40oz not 32oz. I just don't think this works unless I'm missing something. Now the 8oz is 25% of what you started with so maybe that could help form an equation. Just my thoughts.

 

Actually, don't you want to solve for S2? Since you want to know what the gravity will be after adding. Or did I miss the point. Or are you saying by observing the changes in gravity when adding a known volume of water, you can then solve for V1 from the changes in S? Hmmm. Useful either way I suppose. Thanks for posting this.
Greg

 

You could solve for any variable by manipulating the equasion. In this case, though--the title is Determining The Water Volume Of. . .. , we're solving for the unknown variable V1--being the total system volume. The premise of the post is that you don't know the system volume.