# CO2 drop checker - nubee question



## MaxAltitude (Mar 14, 2017)

Hi guys,

My CO2 drop checker finally arrived on the sailboat from overseas... I was excited to get it set up and quickly looked at the indicator solution bottle that said to use 15 drops. I quickly put in 15 drops then put it in my tank. Then I found the info online for my drop checker and it said to use 5 drops. It's been in the tank overnight and hasn't changed color. I suspect low CO2 until I get my CO2 injection set up which is likely why it hasn't changed color. But I was just wondering if it will matter that I put in 15 drops instead of 5. (bought online one instead of local because it might look a little bit nicer.)


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## Seattle_Aquarist (Nov 27, 2018)

Hi @MaxAltitude,

For a drop checker to correctly reflect the CO2 ppm it should be filled about 1/2 way with water that has a carbonate hardness of 4.0 dKH. Then add 5 drops of the indicator solution (Bromthymol Blue). It takes about 24 hours for the indicator solution in the drop checker to correctly reflect the ppm of CO2. Here is the chart to help you determine the ppm. With 4.0 dKH water a green color would indicate 30ppm of CO2









If you don't want to mix up your own 4.0 dKH water then you can purchase pre-mixed 4.0 dKH indicator by Fluval for about $9 US.


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## MaxAltitude (Mar 14, 2017)

Now I seem a little bit more confused. This drop checker also comes with the CO2 indicator solution, and the instructions state to put the indicator solution into the drop checker. You say I would also need water that has a carbonate hardness of 4.0 dKH for this? Why would the instruction not indicate that? Or is the indicator solution that comes with it already mixed with some water that has a carbonate hardness of 4.0 dKH? Which might be different than using straight Bromthymol Blue?


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## Seattle_Aquarist (Nov 27, 2018)

MaxAltitude said:


> Now I seem a little bit more confused. This drop checker also comes with the CO2 indicator solution, and the instructions state to put the indicator solution into the drop checker. You say I would also need water that has a carbonate hardness of 4.0 dKH for this? Why would the instruction not indicate that? Or is the indicator solution that comes with it already mixed with some water that has a carbonate hardness of 4.0 dKH? Which might be different than using straight Bromthymol Blue?
> View attachment 175362


Hi @MaxAltitude,

I have also purchased drop checkers from overseas (Aquatic Magic), but never plants. Typically they come with a chart and a bottle of "Indicator Solution" which is actually just Bromthymol Blue (same stuff used for pH test kits). It is not 'pre-mixed' with 4.0 dKH water. Possibly your seller is different.


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