Calculate water volume by concentration of ???

[Larry L]

Whenever I need to dose based on system water volume, I know the tank volume but I'm never confident that I've correctly accounted for additional sump/overflow/plumbing volume, or for displacement by rocks/substrate/corals, etc. So I had a thought...

Assuming I have some "whatever" that is reef safe and readily dissolved, it seems like I should be able to measure an initial concentration of that "whatever", add a known quantity of it to the tank, measure the new concentration, and calculate the actual system water volume from the change in concentration.

What might be be a good substance to use as the "whatever"? It would have to be something harmless, something where the levels are not affected by reef chemistry (at least over the period of time while the new concentration reached equilibrium), and something you could measure accurately and precisely enough to make for a good calculation.


Thanks!
Larry

 

[JimWelsh]

While I've contemplated doing this myself, I have not done it yet, but my best candidate for the "whatever" would be magnesium, with calcium as a close second. In either case, one would obviously allow the level to drop to some lower limit of desirability first. In the case of magnesium, I would be using very good quality products, due to the concern over ammonia being a contaminant in tech grade magnesium chloride products. A key factor you note is the ability to measure "whatever" with sufficient accuracy and precision. I have developed DIY titration methods for magnesium and calcium that are significantly more precise than typical hobbyist test kits.

Another approach might be to actually use H2O as the "whatever" since sudden salinity drops, within reason, are relatively easy for livestock to handle. Again, you would need to be able to measure salinity with sufficient resolution for this exercise to be useful. The sticky thread at the top of this forum on Salinity Determination by Density discusses a method that might permit a sufficiently precise salinity determination method one might use to make this approach feasible.

Whatever method you use for measuring the "whatever", remember that taking the average of repeated measurements is your friend.

 

[Randy Holmes-Farley Verified Community Expert]

FWIW, there are different water volumes you might be interested in.

Do you count pore water in the live rock? Water in the live sand? How long would you wait for your chemical to penetrate these?

Sand alone could have several gallons of water in it. Sand likely packs better than spheres, but packing identical spherical grains will have at least 26% water volume.

FWIW, my guess is that most people cannot measure most things accurately enough to do that much better than measuring the tank dimensions and subtracting for objects in the water by estimate without adding unusual things to the water, such as light absorbing dyes.