Comment by Steven Walker on June 4, 2012 at 1:09am

this is called a drop checker.  the bottom chamber contains reference solution and the top chamber contains indicator solution.  The color on the bottom chamber does not change and the color indicates 30 ppm which is ideal for plant growth without harming fish (it stays an emerald green color).  The indicator solution in the top chamber actually indicates what concentration the co2 is at.  If it is green, it is the same color as the reference solution, it's approx. 30 ppm.  If it is more yellow then it is > than 30 ppm and co2 needs to be turned down.  If it is more blue then the reference solution, it is < than 30 ppm and co2 needs to be turned up.  This particular drop checker is made by Cal Aqua and is a much higher quality version than normally sold.

Comment by Steven Walker on June 7, 2012 at 7:39pm

You're welcome.  :)

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