Dumb Question, but HOW TO consider /calculate tank VOLUME for dosing?

[Megability]

Seems like I should know this already but the more I think about it, I'd like confirmation - how should I calculate tank volume for calculating various doses?

So I have the RedSea Reefer 625, which is listed as 131 gallons of the display tank, and 32 gallons in the sump, and then I have about 100 lbs of MarcoRock between the display and some in the sump, and then 3 MarinePure Blocks too, and of course equipment.

Some say the tank manufacturers inflate their listed tank volume because they use outside dimensions instead of internal, and I know MarcoRock is dense and heavy, so maybe displaces more water than others or live rock, but then the MarinePure Blocks are super porous and probably don't displace much water at all.

A volume estimator tool I found says all that rock, blocks, and even sand only takes away about 10 gallons of water from the total volume, but that doesn't sound like much.

Aquarium System Volume Calculator

So... thoughts?

 

[DJF]

One ballpark method I’ve heard is if you have a regular sump, don’t count it and use the tank volume- it’s not very scientific. I did that and haven’t experienced issues with my dosing quantity.

 

[Troylee]

Since your sump is only about 16gal at half capacity I’d delete that and say your tank 132 gallons would be sufficient for dosing… like mentioned above me that’s a great starting point.. my system has about 200 pounds of rock and 120 pounds of sand and it displaced my water by 30 gallons.

My tank volume is 275 with a 125 gallon sump.

 

[rhitee93]

I can give you one datapoint. I just started my system a month ago and measured the water it took to fill it.

I have a nominally 120g tank, and a nominally 30 gallon sump. Total water to fill the system to the proper level for running was 108 gallons. That is with 125lbs of various rock in the system and 80lbs of sand.

 

[PotatoPig]

Option A: Be very careful to measure water when putting it in.
Option B: Drain it while carefully measuring how much you’re pulling out.
Option C: Get a very accurate salinity measurement tool and add a measured quantity of salt. Measure salinity before/after, then calculate from that what the volume of water must be.
Option D: If you know the weight of rock and sand you can work out their density and hence their volume. Then subtract that from the calculated volume taking the inside measurements from the glass.

 

[Troylee]

To answer your question thou you could measure the inside of the tank.. LxWxH divide by 231 and that gives you the exact volume of water. Same with the sump! Just have to figure rock and pump displacement.

 

[Megability]

Option A: Be very careful to measure water when putting it in.
Option B: Drain it while carefully measuring how much you’re pulling out.
Option C: Get a very accurate salinity measurement tool and add a measured quantity of salt. Measure salinity before/after, then calculate from that what the volume of water must be.
Option D: If you know the weight of rock and sand you can work out their density and hence their volume. Then subtract that from the calculated volume taking the inside measurements from the glass.

Thanks, so if going with Option D I should probably trust the estimator that my rock and sand, etc., really only reduce volume by 10 gallons or so - seems low but maybe the best estimate

 

[exnisstech]

I can give you one datapoint. I just started my system a month ago and measured the water it took to fill it.

^this^ is the exact way to do it and be accurate. But of course it has to be done at the time of the original fill.

 

[Mr. Roboto]

Take all the water out and add it back gallon by gallon. It's what I did.

 

[dschuffert]

I have always estimated. My display tank is 242 gallons with the tank and sump. I estimate the displacement of the rockwork and then go with that number. It has always worked for me.

 

[jda]

Take the inside dimensions of the tank, the actual volume of water in the sump and subtract like 10% for rocks. This is close enough. There is no need to be more precise than this.

I have seen people try and figure out the displacement of their heaters, pumps, skimmer walls, etc. but while this is all doable with math, I have no idea what purpose it serves.

 

[MnFish1]

Take the inside dimensions of the tank, the actual volume of water in the sump and subtract like 10% for rocks. This is close enough. There is no need to be more precise than this.

I have seen people try and figure out the displacement of their heaters, pumps, skimmer walls, etc. but while this is all doable with math, I have no idea what purpose it serves.

Not sure that 10% is the right number - but you're absolutely correct. First - most things do not require an exact 'tank + sump' volume. Second - you can also measure (as many have said) - the gallons added - but then also remember - as your tank matures - there will be coral growth, and less water.

 

[Pistondog]

Dosing what?
If alk-ca-mag take a guess within 10 to 20%. Dose, measure and adjust dose.

 

[Waters]

I have always just taken the tank volume and omitted the sump, figuring the sump and live rock in the DT would cancel each other out.

 

[radiata]

The REAL ANSWER is right here on R2R! This shows you how to use chemical tests to calculate your real water volume:
https://www.reef2reef.com/ams/beginner-series-1-what-is-your-actual-water-volume.574/

The equations aren't as complicated as they first look.

 

[MnFish1]

The REAL ANSWER is right here on R2R! This shows you how to use chemical tests to calculate your real water volume:
https://www.reef2reef.com/ams/beginner-series-1-what-is-your-actual-water-volume.574/

The equations aren't as complicated as they first look.

This is actually a good find. Having said that - and I'm sure the author would agree. - You're relying on tests done on a chemical addition (so there is a pre-test, and a post test) - An error in either could cause a big problem. Now - IF one had a perfect test (which is not possible) - this is an excellent idea - and something I hadn't thought of. I would not use Calcium - since most tests are difficult to read - I might use a hanna checker with alkalinity, for example.

 

[MnFish1]

I have always just taken the tank volume and omitted the sump, figuring the sump and live rock in the DT would cancel each other out.

This is not a good estimate - for a couple reasons - first - some people have (believe it or not) - a 300 gallon tank and a 50 gallon sump. A friend has a 100 gallon tank and a 100 gallon sump. But - In truth - except for dosing medications (which is not usually recommended in display tanks) - the chemicals can be easily measured. And most people say - estimate the volume on the low side - you can always add more - but it can be more difficult to take out without multiple water changes

 

[radiata]

This is actually a good find. Having said that - and I'm sure the author would agree. - You're relying on tests done on a chemical addition (so there is a pre-test, and a post test) - An error in either could cause a big problem. Now - IF one had a perfect test (which is not possible) - this is an excellent idea - and something I hadn't thought of. I would not use Calcium - since most tests are difficult to read - I might use a hanna checker with alkalinity, for example.

I used the suggested Red Sea calcium and a Salifert test kit. You will need a good kitchen scale to weigh the calcium. The results I get have held up when I add individual replacement elements with good math instructions like Britewell's. I test, calculate and add the dosage I need to get where I want to be, and get the expected results when I test again.

 

[MnFish1]

I used the suggested Red Sea calcium and a Salifert test kit. You will need a good kitchen scale to weigh the calcium. The results I get have held up when I add individual replacement elements with good math instructions like Britewell's. I test, calculate and add the dosage I need to get where I want to be, and get the expected results when I test again.

As I said in my answer - its a good answer

 

[Waters]

This is not a good estimate - for a couple reasons - first - some people have (believe it or not) - a 300 gallon tank and a 50 gallon sump. A friend has a 100 gallon tank and a 100 gallon sump. But - In truth - except for dosing medications (which is not usually recommended in display tanks) - the chemicals can be easily measured. And most people say - estimate the volume on the low side - you can always add more - but it can be more difficult to take out without multiple water changes

For me.....works perfectly lol....but you are correct. Sump vs tank size obviously plays a huge part.