How much water do you really have in your tank? HINT: it's not what you think.

[revhtree]

Knowing the amount of water you actually have in your aquarium is pretty important considering it can impact quite a few areas of reef keeping. But it's not as easy as knowing the amount of gallons or liters the aquarium manufacturer says that your tank will hold. How much of the "liquid" space is taken up by your live rock and sand? How close to the top edge does the water need to be? What about your sump and the equipment in it? The plumbing etc. etc. etc? How important is it really? Let's talk about it.

Did you know that tank manufacturers measure the outside of the glass when calculating tank volume when the inside of the glass gives a more accurate measurement?

1. How much water volume do you think you actually have in your main display and what was the manufacturers advertised gallons or liters?

2. How important is it to have an accurate measurement of water volume in your system?

image via @Triton USA

 

[kartrsu]

Pondered this too when I started my IM Fusion 20. Before I got RODI, I was using distilled water from the grocery store. It was hard enough to find 20 gallons of distilled water, but I was adamant I needed it. Started filling the tank and ended up with 5 gallons left over. I was a bit disappointed realizing the tank was actually holding 75% of marketed water volume, but I got over it. It was important to know though from a dosing perspective (e.g. targeting N / P levels to fight dinos). I wonder how it plays out with bigger tanks and if the difference is less than in smaller tanks.

 

[kartrsu]

Oh, I'd also add that it made water changes deceptively larger than I expected. I use home depot buckets for water changes and I make a full 5 gallons each time I do a water change. A full bucket water change would have been only 25% at marketed volume, but is actually 33% at actual water volume. So if you're doing frequent small water changes, you could be changing more water than you think if you're basing on marketed volume, which makes swings in parameters more drastic than you'd imagine.

 

[Paul B]

I voted it s not that important. If you are medication something it will be important but a tank with no problems, I can't see that it matters.

 

[WiscoFishNut]

1. Between the DT and sump, 63 gallons. I'm pretty confident about that #. The DT is listed as 60g and the sump is listed as a 20g.

2. For me I feel that having an accurate measurement is important so I can dose properly. I might be a bit paranoid, but I'm new to the hobby so I'm trying to mitigate potential mistakes as much as possible lol

 

[Zionas]

Any way of calculating how much water our tanks really hold? Formulas?

 

[vetteguy53081]

1. How much water volume do you think you actually have in your main display and what was the manufacturers advertised gallons or liters?

Tank is 660g and sump is 140g for total of 800 gallons. When I set tank up and added rock and coral, I used enough salt for 710 gallons.


2. How important is it to have an accurate measurement of water volume in your system?

It's VERY important in some aspects. When it comes to dosing or medicating, we have to go by USEABLE gallons. An example would be a 100 gallon tank. With rock and other components, there will be in essence 80 USEABLE gallons so when treating for lets say ich, you are treating 80 gallons not 100, and here you can see why its' so easy to overdose

 

[Paul B]

I still don't think it matters because if we have rocks and corals, we can't know exactly how much water is in there. We know that we have a 100 or fifty gallon tank but we have to guess the actual volume.
Also we dose depending on the amount and type of coral. Then we test. If we have no coral, we don't even have to dose.

Every tank, no matter the amount of water would be different and if we were to medicate for ich, it probably would not be in a reef tank with rocks, sand and coral so we would know the actual volume because we bought the tank, or we could measure it to determine the gallons.

 

[sfin52]

I have a 90 gallon just upgraded from a 75. With rock and sand I think I'm close to 75. That's just a guess. If dosing it could be a concern. I don't so no big deal. We test we dose we test.

 

[Deezill]

SO my tank is a 210-gallon Aqueon and my sump is a 60-gallon Bashsea. I have figured out my water volume to be 240 gallons. I know this is correct because when I am doing my 2 part dosing I hit my aimed desired amount on the head.
This is why it's so important for me to know the water amount. I have 158 pounds of now live rock, and I have 100 pounds of live sand. at least Carib sea says its live, I don't know. it should be live now after all this time. so yep 240 gallons.

 

[MastaMind82]

My 55 with 20 sump has exactly 55 gallons of water in it. When I first filled the tank I had kept track of how many gallons of water was actually going in since I wanted to know the true number. I feel it's good to know how much water is actually there, for instance when I was deciding what size heaters I needed it was nice knowing how much water I had in the system.

 

[Regular_Reefer]

My display is 60g with a 30g sump. Taking into account rock and equipment I’m roughly sitting at 70g total volume. I recorded as I filled the system for the first time so I would know. I feel like it’s pretty important to know, especially as this is my first tank. It was mostly important during the cycle since I dosed ammonium chloride for a fish less cycle but now that it’s up and running the only thing I can think that it will affect is water changes. I’m going to try and keep the system as simple as possible so I don’t plan on dosing and I have a hospital tank if anything needed medicated.

 

[Reefs and Geeks]

It's important for dosing, but if you don't mind some tedious work, you can get a pretty close estimate by measuring before and after dosing. Step 1-accuratly measure your aquarium's alkalinity (or other parameter you can measure accuratly). Step 2, guess your system's water volume. Step 3, calculate exactly how much alk 2 part you need to dose to raise alk by 1dkh, (or whatever rise you're comfortable with) and dose that amount. Step 4, wait 30-45minutes and test again. If your alk raised exactly as much as it should have from the dose, than your estimated water volume is correct. If not, you can either work backwards and calculate how much water volume you would need to have to get the alk rise you saw, or adjust your estimate and try again a few days later after your alk is stable and back to normal.

 

[Glass Algae]

Knowing the amount of water you actually have in your aquarium is pretty important considering it can impact quite a few areas of reef keeping. But it's not as easy as knowing the amount of gallons or liters the aquarium manufacturer says that your tank will hold. How much of the "liquid" space is taken up by your live rock and sand? How close to the top edge does the water need to be? What about your sump and the equipment in it? The plumbing etc. etc. etc? How important is it really? Let's talk about it.

Did you know that tank manufacturers measure the outside of the glass when calculating tank volume when the inside of the glass gives a more accurate measurement?

1. How much water volume do you think you actually have in your main display and what was the manufacturers advertised gallons or liters?

2. How important is it to have an accurate measurement of water volume in your system?

image via @Triton USA

One of my biggest regrets was not paying more attention to how much water initially went into my set up

 

[JCTReefer]

In my current 54 corner I have 57 gallons. That includes the 15 gallon sump water height. When I set up the tank I measured gallon by gallon with all equipment, rock, substrate in place. It’s really difficult to guess how much rock and substrate will displace. Too many variables there. Different rocks, different porosity. How much water will different rocks absorb. BRS did a video on this. But still each rock is unique. Most people’s rock work is bigger towards the bottom of the tank with less as you go upwards. I have pillar like structures in my tank and was curious of my water volume inch by inch vertically. So is there less water per square inch in the lower parts as opposed to the upper parts. And of course once you get above the rock work it’s a no brainer. My new tank dimensions are 72x24x28. So 209.45 gallons right. Wrong, the actual internal tank dimensions are 71x22.5x28. 1/2 inch glass used on the side panels and 5/8 used on the front and back. So 193.6 gallons. That’s a big difference. So when I get to the point of actually filling this tank, I’ll do it the same way as my current setup. Measuring gallon my gallon and taking notes along the way. If not I’ll forget. I also weigh my rock structures also. I’m crazy like that. Haha. Being able to dose properly is very important to me. Based on the BRS calculator, I’m spot on when dosing. I tested this multiply times when getting my alkalinity adjusted in the beginning. Alk consumption does change over time, but I know I can plug in my numbers and it will get me very very close.
I also think knowing the approximate water volume makes it easier when choosing a skimmer.

 

[Apropor]

I think it’s important to have a general idea the volume. I have 57g display w 20g sump. My guess is approximately 58g. With testing along with careful dosing all should be pretty stable.

 

[DivingTheWorld]

I chose very important. As others have mentioned, it's important for dosing. Sometimes I have to add Cal/Alk and when using the BRS calculator I need to know the actual volume to make a correct measurement. When it comes to medications, it's vitally important. Dosing things like Vibrant or Fluconozole can be deadly if using too much. ;Dead

I find that tank manufacturers never list the actual volume. It's an approximation. My tank is an 80g with a 25g sump. That said, my actual water volume is about 89g. When I originally set up my tank, I estimated the water volume based on actual interior dimensions, taking away for things like my starboard insert. I also measured the water displaced when I added my rocks to the display. But obviously corals have grown and there are other things like pumps , etc. so nothing is perfect. But 89g is much closer than 105g and based on my testing of Cal/Alk dosing I'm very close. ;Woot

 

[Snoopy 67]

Custom here so internal measurements give me 252 gallons.
Rock was in when filled so it's 210 to the overflow boxes before they fill.
Each box is 5 so that's 220 & the sump runs @ 38 gallons making me @ 258 gallons.
I did add more rock so I use 240 as my base line.

 

[Bleigh]

I think it may be important when you first start dosing. I always dose less than I should though. Then I adjust from there. Did the amount I put it make the chemical go up more or less than I expected? Then I just adjust from there. Up take makes a huge difference for dosing, and there's really no way that I am aware of to know daily changes in uptake. Even if you knew your exact water volume to the mL, you'd have to make adjustments based on uptake.

 

[Brew12]

1. How much water volume do you think you actually have in your main display and what was the manufacturers advertised gallons or liters?

187g DT, 39g sump. Actual water volume of roughly 165g

2. How important is it to have an accurate measurement of water volume in your system?

I don't feel it is important at all. Like others, I based my actual volume based on chemistry values but I'm sure it isn't very accurate. Hobby test kits for alkalinity and calcium aren't accurate enough to get you within 10%, even if you measured out your 2 part chemicals perfectly. Assuming some flaws in measuring your 2 part, and you could be off even further. Of course, it could also get you closer.