# Co2 Drop checker position. Is it 10cm to 15cm from the surface OR 2cm to 3cm from the substrate?



## Zak Rafik (2 Sep 2014)

Hi everyone,

What is the best position to place the Co2 drop checker in a planted tank? I have read from two reliable sources with vast difference of opinion on this matter. I don’t wish to name them as I don’t want to point fingers but rather learn from their experience.

One (A) says to place the drop checker 10 to 15 cm from the water surface. This is the method which I’m practicing and I’m sure many are doing so too.

The other one (B) says to place the drop checker 2 to 3 cm from the substrate. The reason being that
when Co2 rises to the top where the drop checker is placed, the colour reading from the Bromothymol Blue solution is false as it may indicate Co2 levels as being higher or as more than enough when in fact, it’s the opposite!

Having said this, we must also bear in mind that one should not get too hung up on the colour change.

The drop checker is a guide only and not 100% accurate. But we have to make sure that even that guidance is as close as possible to the actual reading.

So I would like to know if fellow members have tried the option B in their tank. And for members who like me are using option A, what’s your take on this? Opinions and feedback shared would be much appreciated.

Maybe I’ll try both positions A & B and see how it goes.

Thanks and Cheers everyone.
Raffik

http://i1295.photobucket.com/albums/b631/Zak_Rafik/IMG_6890_zpsb65e32e2.jpg


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## tim (2 Sep 2014)

I position mine wherever it's easiest to read, as you said it's just a guide.


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## ceg4048 (2 Sep 2014)

It's exactly as Tim suggests. It doesn't matter where you put the DC. It's only a guide and whatever color it reads, if your plants are doing well then whatever color it is and whatever position it is in is the position and color for you. If your plants are not doing well then it doesn't really matter what position or what color it is.

CO2 concentration is not homogeneous in any tank. If you could measure and plot concentration values in X, Y and Z coordinates you would see immediately that there are different values all over the tank. Additionally, the DC only tells you what the value was a few hours ago. It's response time is very slow. So, if you generally have a green DC and one day you walk into the room and see that it is blue or yellow, then you know that something has changed and that you need to investigate. The DC does not know what is correct, only you can know that by observing the health of the plants and fish.

Cheers,


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