How Do Drop Checkers Work?

[gt568]

I don't really understand how these work. Can somebody explain? Once you add the reagent and turn it upside down it's not in contact with the water so how does it work?

And secondly are they any good?

 

[Underwurlde]

As far as I understand it, the CO2 escapes from the tank water into the trapped air bubble and is absorbed by the solution in the bulb (over time, things much reach an equilibrium), the CO2 level in the tank water and the bulb will equalise over a period of a couple of hours.

The reason for using a solution made up to a specified KH, is that in the tank other factors can influence KH. This will lead to errors when comparing KH & pH on the various charts (CO2 measurements can be a function of pH and KH).

Therefire the pH of the solution will change as the CO2 is absorbed. Most pH test kits show a green colour for a pH value of 6.6. Using the normal CO2 charts you can see that a KH of 4.0dKH and pH of 6.6 gives a CO2 reading of 30ppm.

The KH of the solution can be adjusted to cater for different CO2 levels. For example if I change the solution to a KH of 5.0dKH, then when the solution goes green (pH of 6.6) the CO2 reading is 37ppm.

Andy

 

[gt568]

I'm not sure I follow about changing the KH of the solution...

If you change the solution to 5dkh how can the co2 go up to 37ppm? Surely changing the solution won't have an effect on the co2 ppm?

 

[Underwurlde]

As you say it won't 'make' CO2..

Surely changing the solution won't have an effect on the co2 ppm?

Therefore, correct.

f you change the solution to 5dkh how can the co2 go up to 37ppm?

I am not saying that. What I am saying is that if a 5dkh hardness solution is used, then the CO2 will have to go to 37ppm for the pH indicator to turn green (thus indicating 37ppm levels in the tank). If 4dkh is used then 30ppm CO2 will make the pH indicator turn green (thus indicating 30ppm levels in the tank)

With these droppers they are indicators for only a certain level of CO2 in the tank. What I'm saying here is that by adjusting the KH solution to suit, you can target any desired level of CO2.

Andy

 

[Squid]

Perhaps you could shed some light on the drop checkers too and their accuracy.. ADA drop checker - £44.99, Boyu drop checker £12.99.. they look the same to me .. so why would i buy one over the other, surely the ADA name is not worth that much more.

Squid

 

[Underwurlde]

Absolutely no bloody difference what-so-ever.

And yes, they seem to think that by stamping something with ADA is OK to charge 4 times more for...

... and for some unknown reason, people pay!

Andy

 

[Squid]

I should trust my instincts.. thanks

 

[gt568]

Right I think I'm getting this, in a sense all the drop checkers are "set" at 6.6 ph and you adjust the KH to get the target CO2, is this right?

Secondly what effect does the KH of my own tank have, it's quite high near 13?

 

[Underwurlde]

Right I think I'm getting this, in a sense all the drop checkers are "set" at 6.6 ph and you adjust the KH to get the target CO2, is this right?

Correct.

Secondly what effect does the KH of my own tank have, it's quite high near 13?

None what so ever.

The idea behind these drop checkers is to make a pure source of KNOWN KH. We need to do this because measuring KH accurately is nigh on impossible to do cheaply.... So we created this isolated source of known KH that is accurately prepared (without the need for measuring). When then monitor the pH of this known reference liquid, & when it indicateds 6.6, bosh that must be 30ppm (or whatever of course) CO2 and now we trust this to be quite an accurate approximation of the actual ppm's in the tank water (time differentials considered).

Andy

 

[gt568]

Right cheers, think I'm getting there.

So I should use the 4dkh liquid then, yet it states in the instructions to use tank water. Why is this?

 

[Underwurlde]

Why is this?

Heaven knows! You will not know what the KH of the water will be....

Andy

 

[Dave Spencer]

Right I think I'm getting this, in a sense all the drop checkers are "set" at 6.6 ph and you adjust the KH to get the target CO2, is this right?

What you start with is demin water which should have a pH of 7. When enough BiCarb is added to the demin water to give it a dKH of 4, the pH will have risen to 7.6. Adding a few drops of Bromo Blue (Nutrafin pH test kit) to the 4dKH reference solution will turn it blue, which corresponds to 7.6 on the test kit colour chart.

Once enough CO2 has been added to the water column to turn the reference solution green, you will see from the test kit colour chart that the pH of the solution is now 6.6. Using the pH/KH charts, you will now see that the pH drop from 7.6 to 6.6 corresponds to a CO2 reading of 30ppm. Voila!

What your drop checker is actually measuring is the pH of the reference solution.

Dave.

 

[gt568]

What your drop checker is actually measuring is the pH of the reference solution.

And that is altered by co2 seeping (for want of a better word) from the tank water to the reference solution?

 

[Underwurlde]

yes!