What is my water volume? Dose to determine?

[DP Reef]

I've been trying keep up with how much actual water I have in my tank/sump system but have lost track with the constant rock/coral/equipment changes.

Think I can test my alk, dose 10ml of ESV, wait a few hours, test again, then calculate actual water volume? Any other additive or way I could test?

[ReeferBill]

What size tank and sump?

[DP Reef]

50g tank with a 20g capacity sump. I'm guessing I have a around 50g actual water but want to know for sure

[disc1]

Your guess is closer than anything you'll get by dosing and testing. The test kit doesn't have the precision to do that.

[ReeferBill]

How many corals do have? I use to add 30ml of each 2 part to my 46 bow. And 38 sump but now I add 60 ml of each because I have a lot of coral growth and 100 lbs of live rock in sump. Corals are growing again. Try 30 ml of each for now to see how your corals do check levels once/ week for adjustment.

[Vinny Kreyling]

When you do a water change measure the difference in height of the water level in the tank after it drains into the sump.
Now if you take out 20 gallons & the level drops 4" you have about 5 gal/ inch.
Sump is easy - LXWXH divided by 231 on inside measurements.

[albano]

Originally Posted by Vinny Kreyling

When you do a water change measure the difference in height of the water level in the tank after it drains into the sump.
Now if you take out 20 gallons & the level drops 4" you have about 5 gal/ inch.

That method cannot give you actual gallons, in a tank containing live rock, sand, overflows, etc.
A simple INSIDE length x width/ 231 =gallons per inch ... BUT, does not account for LR, etc.

[jimmcwibb]

Sure you can try dosing. Do it with Ca, Mg and Alk and you'd get three values. See if they give roughly the same volume.

[bertoni]

I agree that using a test kit won't give much precision. I can't think of a good way to get an accurate water volume estimate, really.

[RAJOD]

The only way to know for sure is to drain your tank and refill it.

So you will have to take your best guess based on tank size, sump and then subtract space from sand and rock.

[DP Reef]

Originally Posted by jimmcwibb

Sure you can try dosing. Do it with Ca, Mg and Alk and you'd get three values. See if they give roughly the same volume.

I will try this method and see what happens. I agree with other posters that there may be no good acurate method as each time I test the results can change slightly and test accuracy is also a problem. I can try this across several tests during the week and take an average. I'll report back for everyone to see what the results look like.

Anyone know which test kit and which test is generally the most precise/accurate?....this is probably heavily debated in other threads

[bertoni]

I think the resolutions of the Salifert kits are as good as any other hobbyist kit of which I'm aware.

[disc1]

Well, forget alkalinity. That would be the worst case since there is the least of it. You'd probably want to use magnesium.

Let's say you want to stay safe, so you try to boost magnesium by 100ppm. So you add enough supplement that you think it will take to do that and then you test. Magnesium test usually has a precision of about 20ppm, meaning the possible readings are 20ppm apart. It can read 1340, 1360, 1380, but it can't read for instance 1374.

So if everything is perfectly done here, you could expect at best a 20% error. In reality mag tests aren't perfect, so we should account for other possible systematic error. If we stay conservative then we'll say maybe you know the magnesium to within 20ppm either way. So a 40ppm error range is a little more realistic than 20ppm. But for your 100ppm addition that's a 40% error.

What does the measurement look like with a 40% error range? Well, let's say the answer comes out to 50 gallons. But you can't call it 50 gallons, you gotta have the plus/minus on there. It's really 50 gallons +/- 20 gallons. So you have something between 30 and 70 gallons of water there.

I'd hazard to guess you already knew the volume to that level of precision. And that's what I meant when I said that your guess would be closer than anything you'd find by dosing and testing.

[ReeferBill]

Albano ,how. Much are you dosing now? Start out with 20-30mls of each to begin with to see what you come UP with at weekly test intervals. Then adjust dose accordingly. When I. Had a 75 gallon reef with 100 lbs of live rock and 60 lbs. of DBS I started I out with 20mls of each 2 part everyday and 20 Mls of mag added to that every third day. That would be a good starting point and go from there.

[DP Reef]

Thanks Disc1 for putting it into perspective as well as giving me more reason to avoid all the testing I had thought of as I left the house this morning....

If I went with 200ppm and assuming its still a 20ppm error margin then it would end up being 45-55. +- 5 gallons is not that bad...but not as accurate as I was hoping it would be

I guess it doesn't really matter, the ultimate reason I was curious is to play with these dosing calculators, but you can always find the dosing you need empirically by trial and error. I don't exactly want to start adding a huge amount of additives just for this purpose. At some point, I'm then just risking coral's health....

Unless there is an additive out there that has no impact to well being of tank inhabitants and can be measured in high precision. At this point, I'm just curious and want to figure out an exact volume!

[DP Reef]

I guess both PH and conductivity measurements are not accurate enough either. Not that these can take any swings!

Magnesium would have been the best option. I've dosed it in the past to kill bryopsis and didn't notice too big of an impact to my tank inhabitants health.