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

[killyfish]

I have just set up a smallish fish only marine tank - the Juwel Rio 350, as the name implies, capacity is 350 litres. I fitted it out with an under gravel filter covered with coral gravel/ crushed shell, 40 lbs. of coral sand, rock decoration - oh and the ‘optional’ protein skimmer which, being a Juwel accessory is large and clumsy, 23kg of inert rock, a few kilos of TMC replica living rock and a sea fan that I have had for at least 40 years and then I measured the water capacity when I filled it up - the total was 222 litres - 48UK ( imperial) gallons. That is 128 litres (28 UK gallons) less than the empty capacity. Obviously this affects stocking capacity and certainly influences medication dosage. Not quite as simple a comparison as rock, sand and protein skimmers all absorb medication, so you still need to keep an eye on copper levels etc. Just shows how much capacity is reduced.

 

[Jax15]

When I was filling my tank for the first time, I had planned to measure how much water went in since I was adding 5g at a time. When the time came, I forgot and lost count.

I really regret this!! If you're setting up a new system, don't forget to do this! It's really your only chance to get a truly accurate measure of actual water volume in your system.

That being said, I think if you can estimate within 5-10% you're probably fine for most things.

 

[schuby]

I believe that actual water volume is important if you have corals and dose to maintain a certain Alkalinity level. As my corals grow, they use more Alkalinity a day. I test twice a week. If my Alk goes down more than .2 dKh (testing at the same time-of-day), then I'll increase my dosage slightly and step up my Alk level using sodium bicarbonate by .1 dKh a day.

Alk seems to be the most dangerous thing to change too fast. If I don't know the actual water volume of my tank and sump, then I could easily overdose my "correction" Alk and cause major harm to my corals.

 

[richarddeweerd]

My tank is 535 liters according to the manufacturer, but it is around 400 liters

 

[Brew12]

Guidelines aren't that precise LOL

I keep a cracked 250g in my garage since they say I need to have a tank that size for the Naso I have in my biocube. ;Troll

 

[thermoJoe]

Guidelines aren't that precise LOL

Lol, yes, I was joking, but the discrepancy between advertised volume and true volume can be pretty big. I have three tanks that have an advertised volume of 131 gal in total, but their measured working volume (not accounting for rock displacement, etc) is only 91 gal. That's 44% less than stated, which is pretty huge difference. So when the tang police say I need at least 120 gal, what they really mean is just need 67 gal, lol

 

[sg88]

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

It is simple math, but does take a little extra playing around. LxWxH of the wet area is the water in your tank in cubic cc or cubic inches (remember your height, or depth, is only to the overflow weir teeth). Then you can convert to your favorite unit of volume by Googling a conversion. The L and W are pretty easy but the volume of the overflow will likely be a little error as the water lever may be a little bit below the weir teeth and the walls and pipe walls take up some space. Now the depth of sand needs to be subtracted out. Again LxWxD is your volume is sand. Water in most sand beds will be a negligible amount relative the dry sand. The key are the rocks. There you get a big bucket that holds all the rock (or a rock or 2 at a time) Fill the buck to the top with water, then dump that water into a bucket that has reasonably accurate measurements and find out how much water you used. Now put your rocks in and add water until you top the bucket out. The left over water is the volume of your rock and is subtracted just like the sand volume. Do the same for your sump remembering that you will run the depth at something other than the total depth.

 

[fishnovice33]

I don’t think it’s that important, it’s just on of those things that’s nice to know.

If manufacturers were exact then so would dimensions. For instance a 60 gallon is 48x15x18. Now a true 60 gallon would be like 48.5x15.5x19. Or they could stick with previous measurements and say it’s only 53 gallons or whatever. I think at some point you’re going to tailor it someway.

I like the fact it’s not exact with cleaner numbers. You’re already adding substrate and coral or other stuff and unless your measuring exactly how much displacement each item and fish causes somehow and subtracting it from total gallons/liters, and never add or remove anything unless you want to recalibrate (doubt 99% people do this) you’re dosing is going to have be dialed from trial and error anyhow.

Just start with underdosing and go from there. It’s pretty easy to not end up over dosing if you start there and pay attention.

Not everyone is a fanatic, in fact most general public aren’t and once you start deviating from clean numbers, confusing starts setting in and sales will probably hurt as well. Just how it is. Yea for us, it’d be nice to know but in the end it’s not that hard to calculate by yourself if you really wanted and I don’t feel it matters too much anyways.

 

[ewanho]

Purchased at 15g
actual closer to 11 after stocking

 

[JLynn]

If you do any kind of dosing - medications, supplements, especially anything that you can’t test for (or can’t test for easily), it is very important to know the actual volume of you tank and system so that you can accurately dose.

It also becomes important if you need to determine the weight of the tank when filled with water, so for example if you want to put a larger aquarium in an upper floor and you need to know if the building can support the weight.

 

[dbowman5]

If you do any kind of dosing - medications, supplements, especially anything that you can’t test for (or can’t test for easily), it is very important to know the actual volume of you tank and system so that you can accurately dose.

It also becomes important if you need to determine the weight of the tank when filled with water, so for example if you want to put a larger aquarium in an upper floor and you need to know if the building can support the weight.

for load calculations i would add the empty weight of the proposed tank and stand (easily found on manufacturers sites)
and the total possible volume of water X 10 lbs. then multiply everything by 1.5 for a safety factor and there you are.


(water is 8.3 lbs per gallon and anything that sinks is heavier; a cubic foot of concrete weighs 150 lbs, a cubic foot of water weighs 62 lbs) if you have 1.5 lbs of rock per gallon in 100 gallons of water you would be displacing 62 lbs of water. so 830 lbs of water plus 150 lbs of rock minus 62 lbs of displaced water equals 918 lbs of combined weight. 9.18 pounds per gallon rounded up to 10 lbs per gallon)

 

[Klyle]

My non expert opinion- it somewhat matters. You need a ballpark to get close. From there, I believe testing matters more. If you’re dosing based on an inaccurate water volume, you’re testing will reflect that and you can correct from there. If you never test anything and just dose, I bet you won’t make it long in this hobby. Unless you’re like the Doogie Howser of reef tanks.

 

[Texas Rick]

I have a 30 gallon JBJ nanotank. But it only fits 28. And after adding rock and sand. Only 25 gallons fit.

 

[walloutlet]

I managed to measure the water in my tank as I set it up with both rock and sand. So I’m comfortable with understanding how much water volume I have .

However, the keener and numbers guy in me then goes, well now I added a skimmer, oh and those corals grew out more and fish have been added and so on, would drive me crazy getting to an exact number. What I realized is that good estimate is what everyone needs. Treating / dosing 100 gallons of water is much different than treating 75 gallons of water.

For reference, I was really surprised that in my “65 gallon” display tank I was only able to fit 50 gallons of water, including the overflow with about 45lbs of rock and 20lbs of sand.

 

[H3rm1tCr@b]

1. How much water volume do you think you actually have in your main display and what was the manufacturers advertised gallons or liters?
Well, I'm pretty sure without the rock and sand I would have 20gal. It was advertised as a 20gal tank after all.

2. How important is it to have an accurate measurement of water volume in your system?
I think it can be pretty important for situations with medicine and dosing. For fish stock I can see it's importance also. For example, if my tank was advertised as lets say a 20gal again but was only somehow 10gal without anything in it, I'd be pretty p*ssed off, not to mention the fact that my fish would crash the system with their waste.

 

[H3rm1tCr@b]

I have a 30 gallon JBJ nanotank. But it only fits 28. And after adding rock and sand. Only 25 gallons fit.

That's annoying! They must have not accounted for the thickness of the glass or something.

 

[Ippyroy]

My DT says 32 and my sump is 40. When I dose, numbers come out correct when I say 45 gallons so that is what I believe it has.

 

[markfmvl]

not sure why you would need to figure the volume in the tank for dosing unless you are trying to meet a target, but even then start where you are at if low set your doser a little higher. Test again in a few days . you want to move things SLOWLY any way.

 

[mkwarner77]

the size of the tank is probably the biggest factor in how important it is. Actual water volume would matter less in large tanks, say over 120 gallons, but in small tank, 50 gallons and less. its a larger factor, dosing in smaller tanks can have a large impact if your off a few gallons.

 

[WVNed]

LOL
Yes you need to have a good idea of how much water is in your system for a whole bunch of reasons.