Drop Checker Question

[Haveagojoe]

Iv'e just bought a drop checker off ebay and I'm slightly confused, with it came a bottle of a yellow liquid and the instructions say half fill the drop checker with tank water then add 4-5 drops of the liquid until the water in the checker turns blue then place in the aquarium where over the next few hours it will start to indicate how much co2 is in the water.Now everywhere I'e read says do not use tank water and when ive followed tne instructions the water in the drop checker stays yellow and does not turn blue as it says it should,ive left the drop checker in the tank overnight and its not changed colour at all its still the same yellow as it was when I put it in,any ideas.

 

[Aqua Marine]

You would have to use your tank water otherwise there would be no way of measuring the CO2 in your tank if you used another water source?!? I have done similar drop tests before for pH etc and all have used tank water samples, mixed with the liquid provided!

 

[ian]

You don't add tank water, you add 4dkh water. Tank water has plenty of stuff in it to throw the drop checker off. I'm on my phone at the min, so struggle linking things, but have a look in the parc section in the planted forum. There is a great write up about drop checkers.

 

[Haveagojoe]

Iv'e read the article about drop checkers on here but am still confused as to why the stuff I got hasn't turned blue I can't see that I am overdoseing with co2 I'm only using the hagen method on a 100 ltr tank.

 

[aaronnorth]

Acids lower the pH of the water, when CO2 dissolves in water it produces carbonic acid (H2CO3). This turns the colour from blue to green, then yellow. When CO2 injection stops, the carbonic acid is convereted back to CO2 (It is an equilibrium reaction).
CO2 + H2O <=> H2CO3 <=> H+ + HCO3 <=> CO3-- + 2H+
This is also depicted by the pH, and the rate of the pH change is depicted by alkalinity.

You already have natural acids being produced in the tank water, so these will affect the result of the colour, hence why your DC is staying yellow, and not turning blue.

Thanks, Aaron

 

[aaronnorth]

You would have to use your tank water otherwise there would be no way of measuring the CO2 in your tank if you used another water source?!? I have done similar drop tests before for pH etc and all have used tank water samples, mixed with the liquid provided!

The easiest way to prove this method wrong is too look at a pH/ KH CO2 relationship chart.

We aim for 30ppm CO2, which as shown by the chart the KH must be 4, and the pH 6.6
Hence why we use 4dkh as a known indicator, so when the DC is green the pH is 6.6 which indicates 30ppm of CO2 is dissolved in the water.

Now assume the water came out of your tap at pH 6.6, and 4 KH. Do you think it is possible to have 30ppm of CO2 leaving your tap water?

Thanks, Aaron