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Re: [APD] drop checker for CO2

> Yes, it does rely upon KH and pH to determine the CO2 level. 
> The  
> difference, and it is a very big difference, is how it does
> it.  The  
> pH and KH being measured is not that of the tank water, but of
> the  
> tiny bit of  water in the device's bulb.  

There is an air gap between the tank water and the drop
checker's water.

So there is no mixing of the reference water/tank water.

The chemicals are cheap etc.

Personally I'm fine with looking at the plants etc, Riccia will
pearl like mad as will many species and grow well.

But this method will help folks wanting to know what range they
have without spending 90$ for a pH meter or pH pen for 30-70$ or
tend to be too lazy to test often.

Like he said though, the accuracy range is likely pretty wide,
10ppm +/- but that's better than many methods afford...........

And this one is cheap and folks can buy or DIY a checker
themselves with plastic and flame.........
   By using distilled water with just bicarbonate
> in it,  
> the pH/KH/CO2 relationship holds true - there are no other
> sources of  
> acidity or alkalinity to upset that relationship.  In fact if
> you set  
> the KH of the water at 4.0, which you can do very accurately,
> by  
> using 4X the sample size and counting each drop of AP test kit
> KH  
> reagent as .25 degrees KH, the indicator color will be green
> at 30  
> ppm of CO2.  Or, if the KH is 5.0 degrees, it will be green at
> about  
> 40 ppm.  The margin of error for the 30 ppm reading,
> considering KH  
> inaccuracy and indicator color ambiguities, is only about a 
> 25 to 40  
> ppm range, and with care, that can be greatly reduced.

I'm not so sure you can reduce it that much, 5ppm+/- on either
side would be good enough and about the best one could hope for.

The issue is the resolve of the color, our eyes just are not
that accurate and there is variation between folk's and what
their preceptions are.

Ask 5 folks what happened and what they saw at a traffic
accident for example..........you will get 5 different stories.

You need a colorimeter to get better resolve etc and a larger
more responsive test air gap there, less distance and larger
area will achieve that.

Also, if any CO2 mist bubbles hit it, you can see a rapid change
that does not necessarily reflect the tank's CO2 ppm available
to the plants. Just the dissolved CO2 ppms.

> So, these devices separate the measurement of CO2 in the tank
> water  
> from any parameter of the tank water except the amount of CO2
> in the  
> tank water.  That is a major step towards accurate CO2
> measurement.   

Yes, it sure breathes life into these devices again.

> Just because it is simple, non-electronic, and an old device,
> does  
> not keep this from being a great idea!   (It isn't my idea,  
> incidentally, although I wish it were.  All I have done is
> recognize  
> why it works, try it out, and publicize it.)
> Vaughn H.

You mean you do not make claim and appropriate it as your own?

Tom Barr


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