Method to confirm the net water volume

[dc88]

Has anyone faced this puzzle as me ?

Say, you want to add some dosage of whatever to your tank, and the instruction on the bottle said, e.g. xml per 100 liter of tank water.

You look at your tank (3ft, 4ft, whatever..) take a measurement tape and measure the external Length and Width and stick the tape in to check the water height (H) and come out some volume number (LxWxH). Wait, there is the glass thickness, isn't it ? So you recalculate it by minus away the glass thickness (d) : (L-2d)x(W-2d)x(H).
Hey, there is driftwood and rock and substrate too, so finally you take a rough guess of maybe 80-90% of the volume you calculated is really water. Thats probably close enough ?

And then I got this idea whether we can use KH measurement to validate the actual water volume ?

- From the internet the general advice is that every 5ml of NaHCO3 to 100 liter of water will raise KH by 2dH.
(I validated that this is still true in my tank with a controlled measurement on a fixed volume of tank water sample)

- So if we prepare a known concentration of NaHCO3 in solution, and add to the tank in incremental amount, and measure the KH changes, should we able to calculate back the effective volume of the water column in the tank if we now know how much ml of NaHCO3 it takes to raise the KH by a known degree ?

Do you think this method make any sense ?
Comment ?

[AquaObsession]

It is too troublesome to determine the exact effective volume of your tank for the purpose of dosing. The rough estimative is enough when dosing fertilisers.

Anyway, the instructions from good brand of fertilizers say that you dose according to plant demand. You need to observe and doze. There is no fixed formulae when it comes to plants, to any living things for that purpose.

[evolim83]

Might be too much hassles to find the net volume.

The recommended dosages would serve only as a guide as each individuals tank has different plant masses.

[Justikanz]

It would be a good guide to use 70-80% of the full tank volume as the actualy water volume.

[dc88]

Thanks everyone.

The main reason is for micro dosing. (Or may be I am over conservative)
I think for dechlorination or adding macro such as Seachem Eq overdosing never a problem.
But I have difficulty to get the LGM level right.
I search this forum and got the DMDD spreadsheet and use that as a guide which everyone has success. So my only suspect of error is my input of tank volume.
And the Fe concentration is dam hard to judge by test kit. (The color chart is different shade of printed purple color but how you compare that with the purple solution in the test tube?)
Do you think composition and concentration wise LGM is about same as Plantex CSM+B, Seachem Flourish or Tropica Master Grow (TMG) ? If yes I will totally ditch the test kit.
(Sorry a bit divert the topic here, but I guess a little related)

[|squee|]

Just estimate for the iron part... iron test kits are very inaccurate I believe.

[taz_boy]

i believe for nutrients...a bit more would not do much harm..so no harm dosing a bit more..