Beginner Series #1: What Is Your Actual Water Volume?

[Greg Gdowski]

Seawitch submitted a new Article:

Beginner Series #1: What Is Your Actual Water Volume?

The author's 90G reef aquarium.

Photo is from the Reef2Reef archives and courtesy of Greg Gdowski, ©2019, All Rights Reserved.

We put a lot of chemicals into our tanks. Many manufacturers tell you to base additions of these chemicals on your tank's volume – but what is that anyway?

What is your tank volume?

In the beginning, this won’t matter that much. Most of us just add up the stated volume of all of our components. In my case, I have a 90-gallon tank, a 60-gallon refugium, and a 30-gallon sump. That’s 180 gallons. Done, why go further?

As you go forward, every product you will put in your tank will give you a dosage (e.g. 1 drop per 100 l of water daily). When I started down the path of creating a Balling method tank, the issue of “tank volume” was always used extremely loosely. Did they mean: 1) system volume, 2) display tank volume, or 3) actual water volume. It confused the heck out of me until I stepped back and realized that every time I put something into the water, it was all about the eventual concentration of that chemical in the water.

It’s sort of like making your favorite cocktail (why does every article I write refer to alcohol?). If you put in twice as much vodka, you will notice it. For some, that is good, for others, perhaps not. The same is true for your corals. It’s really just best to get the recipe correct.

So, what is your water volume? Seems easy, right? You have sand, corals, rocks, filters, skimmers, pvc pipes, heaters, among other things occupying the space in your stated tank volume that are indeed NOT water. How much volume is that? How much are you off? More importantly, how in the world are you going to figure that out?

If you are like me, you were so excited to fill the tank on the first day that you didn’t even think of measuring how much water you put in. Now you are in a conundrum; it's full of water with fish and corals. You are certainly not going to empty it to figure that out. What are you going to do? That is what this short article is all about.

Once you hear the solution, you will likely say, why didn’t I think of that? For me, it was more like, why didn’t I think of that 10 years ago. I’m sure I’m not the first one to think of this solution, but I thought it was worthwhile to put it out there, likely, again.

Periodic Table of Elements

This image is a royalty-free image from Pixabay.

Using chemical tests as a method for determining water volume.

Here it is in a nutshell. I put in a specific amount of chemical into my tank. I measure the chemical concentration, before and after I put the chemical into the tank. I use the resulting change in concentration to estimate the water volume based on the manufacturers stated dosing prescription.

Let’s run through an example.

I occasionally dose calcium chloride in my tank to set the overall Ca+ level in my tank. I use Red Sea Reef Foundation A (CoralVue). Their stated dosing prescription is as follows:

1 gram will raise the Ca level of 100 liters (26.4 gallons) by 3.6ppm.

Translating that dosage into a formula yields;

Where: VW is the volume of water, DCa is the change in Ca+ concentration, and DCaCl2 is the dosage of calcium chloride.

Let’s say you measured the Ca+ level in your tank and it was 370ppm. Being on the low side, you might want to raise the Ca+ level in your tank by 50ppm. Based on the formula, you might be inclined to dose 94.7 grams in my 180-gallon system in order to raise the concentration by 50ppm. If the estimate of your tank water volume was too high, you might end up raising the concentration by more than 50ppm.

The best way to do this is by using a two-dose strategy that results in first estimating your water volume. Start with dosing an amount that is substantially lower than you think you would need, which you can accurately measure using your scale. I started with 60 grams. I then measured the change in concentration as the difference between the Calcium tests that I did before (370ppm) I added the dose to the tank and after (405ppm) I added the dose to the tank.

Let’s rearrange the formula and solve for water volume:

Based on the outcome of the first dose, I still need to dose additional calcium chloride in order to raise the calcium by another 15ppm in order to achieve 420ppm. This is done by using the new estimate of water volume (163 gallons).

There are a lot of formulas on this page, but it’s really not all that complicated. In the end, had I put in 94.7 grams of calcium chloride, I would have only been off by less than five grams. That would have raised the Ca concentration by 55.2ppm instead of 50ppm. I ended up putting in 60+25.7 grams because this little experiment showed that I actually have a total volume of 163 gallons instead of my initial estimate of 180 gallons.

As you read this, you are probably saying that was a lot of effort to eliminate about 10% of error. I concur that you would be correct, in the short term. However, when you start dosing over long periods of time, small errors perpetuate and grow over time. After you do this once, everything you dose will be closer to what the manufacturer intended for you to put in the tank!

Until next time,

Happy reefing!

Greg

References

CoralVue. "Red Sea Reef Foundation A. Red Sea’s CALCIUM+ contains blended salts of calcium and strontium in the ratio required by corals and is part of Red Sea’s complete Reef Care Program.". from https://www.coralvue.com/red-sea-reef-foundation-a-1kg-powder.

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Author Profile: Greg Gdowski, Ph.D.

Greg has 20 years of aquarium experience, and he has been keeping reef aquariums for the past 10 years. A photo of his current 90G is at the top of this article. He and his wife are also both dog lovers and have two special-needs Vizslas at home.

Greg is also the Executive Director of the Center for Medical Technology and Innovation and Associate Professor in the Department of Biomedical Engineering at University of Rochester.

 

[Matt Carden]

I would add that my 5'x2'x2' tank is sold as a 150 gallon tank but those measurements are outside dimensions with 1/2" glass and an actual water height of 21", is actually only ~100 gallons depending on how much return flow I have.

 

[revhtree]

This is great and something I always think about when I'm dosing something! HA!

 

[Seawitch]

This is great and something I always think about when I'm dosing something! HA!

Yeah, I've always wondered if people actually count the gallons of water that are going into their tanks for the first time and know exactly how much is in there.

 

[Daniel@R2R]

Thanks so much for this @Greg Gdowski! We appreciate you sharing your knowledge with the community! Great write-up!

 

[Greg Gdowski]

Isn't funny how something so simple escapes us.... Thanks everyone.

 

[JoshKReef]

What is a good amount of time to wait after dosing to re-measure? You want to wait long enough so that it makes it everywhere, but not long enough for consumption to have impacted your numbers.

 

[Jay Norris]

This past year , I did a complete overhaul of my system, and when I was finished adding the new sand and placing back my live rock, I added 575 gallons to my system, and believe me that was a little work to collect all that water, as I had to make 4 trips to collect it, but we did catch Dolphin every trip for a nice dinner and few nice smoked fish adventures to. According to my tank measurements the volume should be around 650 gallons, also I don't fill my Fuge and Sump to the top, so that explains a lot of the difference.

 

[Hemmdog]

Brilliant

 

[Greg Gdowski]

This past year , I did a complete overhaul of my system, and when I was finished adding the new sand and placing back my live rock, I added 575 gallons to my system, and believe me that was a little work to collect all that water, as I had to make 4 trips to collect it, but we did catch Dolphin every trip for a nice dinner and few nice smoked fish adventures to. According to my tank measurements the volume should be around 650 gallons, also I don't fill my Fuge and Sump to the top, so that explains a lot of the difference.

650 Gallons! Wow. Thats a lot of water.

 

[Greg Gdowski]

What is a good amount of time to wait after dosing to re-measure? You want to wait long enough so that it makes it everywhere, but not long enough for consumption to have impacted your numbers.

It depends on your system and how fast your pump turns over the water. In my case, I waited a few hours. It was during the dark cycle of my tank while calcium uptake might be expected to be minimal.

 

[CDavmd]

Excellent application of general Chemistry!
One caveat however, the result will be highly dependent on the accuracy and repeatability of the calcium measurement.

Many of our hobby test kits have a wide margin of error when calcium is in the lower end (<400) or when measuring levels too close to each other.

Also the hobbiests’ methods can introduce errors.

To decrease this source of error I would make sure the amount added will result in a significant change in calcium. I would also repeat the measurements 3X and subsequently repeat the process 2-3 times.

Probably overkill but ....but I guess I’m just traumatized by my old college Quant Chem professor

Great post! Cheers

 

[Greg Gdowski]

Excellent application of general Chemistry!
One caveat however, the result will be highly dependent on the accuracy and repeatability of the calcium measurement.

Many of our hobby test kits have a wide margin of error when calcium is in the lower end (<400) or when measuring levels too close to each other.

Also the hobbiests’ methods can introduce errors.

To decrease this source of error I would make sure the amount added will result in a significant change in calcium. I would also repeat the measurements 3X and subsequently repeat the process 2-3 times.

Probably overkill but ....but I guess I’m just traumatized by my old college Quant Chem professor

Great post! Cheers

Absolutely! I thought about adding a section to the article about sources of error. Thank you for bringing that up! I used a red sea test kit that has about 5% accuracy. I did wonder if I would have to repeat the test to reduce noise. I'm pretty good about doing the tests the same way. A Hanna test kit that auto reads the color change might be more accurate. It would at least reduce the error in the operator estimating color changes.

As a bit of a teaser for my next article, I used the same tank volume estimate (163 gallons) to execute an alkalinity change. In this case, I added Aquaforest chemicals -- using their prescription. I then measured the change in alkalinity (ie. with a different test kit than the Ca test kit I used in the article). My target was to move the Alkalinity by 1dKH. Here is the result. The two measurements were taken about 1hr apart. I was pretty thrilled to see it match as best as I could detect with the Red Sea Alkalinity test. In case you are wondering, there is a reason why the dKH is low in that picture --- that is the topic of the next article!

Other sources of error could include the chemicals you add. I primarily use powder forms of the chemicals because evaporation can affect concentrations within a bottle. I almost always mix my own. Chemical test kits also expire -- for the exact same reason (evaporation of titration fluids).

 

[CDavmd]

Absolutely! I thought about adding a section to the article about sources of error. Thank you for bringing that up! I used a red sea test kit that has about 5% accuracy. I did wonder if I would have to repeat the test to reduce noise. I'm pretty good about doing the tests the same way. A Hanna test kit that auto reads the color change might be more accurate. It would at least reduce the error in the operator estimating color changes.

As a bit of a teaser for my next article, I used the same tank volume estimate (163 gallons) to execute an alkalinity change. In this case, I added Aquaforest chemicals -- using their prescription. I then measured the change of alkalinity (ie. with a different test kit than the Ca test kit I used in the article). My target was to move the Alkalinity by 1dKH. Here is the result. The two measurements were taken about 1hr apart. I was pretty thrilled to see it match as best as I could detect with the Red Sea Alkalinity test. In case you are wondering, there is a reason why the dKH is low in that picture --- that is the topic of the next article!

Other sources of error could include the chemicals you add. I primarily use powder forms of the chemicals because evaporation can affect concentrations within a bottle. I almost always mix my own. Chemical test kits also expire -- for the exact same reason (evaporation of titration fluids).

great stuff!

 

[Captain Quint]

Love the article and thread!

Yup, ID of the tank, OF's sump skimmer upload and asking what TUWV to some of my friends have given me the look of as if I have a third eye. lol

 

[crabbydan]

on my most recent tank i actually counted every gallon added. My total water volume on this tank is 132 gallons.

 

[Bill Howard]

Do you think you could use the change in salinity vs the amount of salt added to do the volume calculation?

 

[Jay Norris]

650 Gallons! Wow. Thats a lot of water.

Yes it was, but it was a lot of fun collecting it, nothing like going water collecting at sunrise on a flat calm Summer day, with gin clear water all around you. Sometimes I wonder why I have an aquarium, when all I need to do is go out to the reefs and enjoy Mother Natures aquarium, but then parts of Fall, Winter and a bit of Spring come, and all this freezing cold weather and water is not conductive for a fun water day wearing shorts and a short sleeve shirts. You see I don't like boating when the wind is blowing over 20mph and the Temps drop into the low 70's or high 60's during the day . Parts of Springs the weather starts to warms up into the 80's, the wind lays down and all returns to normal, then comes Summer, the temps are in the 90"s the wind is hardly blowing and you have the perfect time of year for diving, the same with the first part of the Fall until the first cold fronts arrive. I due still collect water during those bitter, and windy cold days when the temp never gets out of the 70's or high 60's, but then these days are reserved for mostly fishing and collecting water, wearing warm foul weather gear helps a lot in enduring these terribly harsh conditions. But I guess it's beats a good day at work any time of the year.

 

[Greg Gdowski]

Do you think you could use the change in salinity vs the amount of salt added to do the volume calculation?

Bill -- theoretically that would work. That said, salinity is something I try to keep pretty steady. If you were doing it first when you were adding salt it would work (ie. going from 1.0 to 1.025). To minimize error, as pointed out by CD earlier, you need to create a significant change in concentration for it to work optimally. If you were changing from 1.024 to 1.025 or 1.026, I don't think you could measure the salinity with enough accuracy for it to work.

 

[ca1ore]

I would add that my 5'x2'x2' tank is sold as a 150 gallon tank but those measurements are outside dimensions with 1/2" glass and an actual water height of 21", is actually only ~100 gallons depending on how much return flow I have.

This is something that has irritated me for years. There are a few tank manufacturers that are more ‘honest’ about net gallons. Customaquariums actually have a table on their site that distinguishes model gallons from actual gallons. As tanks get larger, the two numbers depart quite significantly. Fortunately it’s trivial to mathematically calculate. Multiply the internal dimensions together in inches and divide that by 231. My current tank would be designated as a 450; 400 gallons of water plus 50 gallons of acrylic.

The only way to calculate displacement beyond that is to do something like the OP suggests. Though I wonder whether absorption by rock and sand messes with the calculation? Frankly, I generally don’t bother. Happy to WAG it.