Water Volume for Dosing

[scott11]

How do you all calculate water volume for dosing purposes? I have a 90 gallon tank, with a sump, but I know I dont have 90+ gallons of water. I think my sump is about 7-10 gallons, with not much in there to displace water, but how do I determine my display volume, when I have several inches of sand and a ton of rock?

I have seen a calculator online before, but did not feel it was accurate.

Any tricks? What do you all do?

[nuttyd]

Doesnt have to be that accurate. Never dose full amount the calculator says. Work up to that amount over a week. Then you get a good idea of how much you need to do daily to maintain levels.

[downbeach]

This is where some trial and error come into play. You'll just have to make a calculated guess, and adjust your dosing based on your results.

[Vinny Kreyling]

This is why you should keep track when you fill the tank.
With rock & sand my 250 held 200 gallons to the bottom of the overflow grates.

[bertoni]

You can measure the alkalinity level, dose, and then measure again to get an idea of how accurate your guess as to the water volume was. For a tank with a sump, I might wait 30 minutes for the supplement to be dispersed, but I'm assuming the sump is reasonably small, no more than 20g of water, and the flow rate is enough to change over the sump a couple of times in that time period.

[scott11]

I think thats part of the problem, I have a fairly low turnover through the sump, so I am worried about testing too soon. Makes it hard to figure out daily usage if I test daily, because I need to try and back out what was consumed that day.

Really not an issue, just wondering if anyone has a good way to estimate actual water volume.

[Vinny Kreyling]

If you can measure a 5 gallon bucket drop the tank 10 gallons.
Measure the distance in inches from start to finish with a stable water line, no surges.
This will give you a measurement to use with the height of the tank.
The same can be done with the sump with either 5 or 10 gallons.

[scott11]

That will not account for the Rock and sand.

[Vinny Kreyling]

It will get you closer than you think, & better than a guess.

[albano]

It would help to use the inside measurements with actual water level depth, to calculate the water volumes of the tank and sump... 90g tank is probably closer to 75g

[oseymour]

I made an educated guess and then made small adjustments to get the proper dose.
Your probably going to be within 10 to 15%.

According to BRS 2 part video I watched a while ago. "If you were trying to raise the calcium 30ppm and you were off by 10%, you only raised it 33ppm and its highly unlikely that your test kit would be able to detect the difference of 3ppm.

EDIT: Here's the video, I started it at the point I was talking about. - https://youtu.be/bVI69xOb_JM?t=243

[hkgar]

This works pretty well.

http://reef.diesyst.com/volcalc/volcalc.html