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Drop Testers - are they reading CO2 or PH ?

tubamanandy

Member
Joined
28 Feb 2013
Messages
362
Location
Thornton, Lancashire
I've got a tank reading PH 7.2-7.3 (Seneye meter) and a Drop Checker showing a really nice lime green.

I thought a drop checker was basically a PH checker ? Is it actually reading the CO2 concentration in my tank or the PH in my tank ?

Can someone clarify
 
Both. They are reading the pH in the water in the drop checker. However as you use a known KH water in there (4dKH) it means that the pH solution will turn green when there's 30ppm CO2 in the water. So indirectly they measure CO2 by measuring the pH of a known KH water where the only outside influence on the pH is the CO2 level.

In your tank other acids and bases will affect the pH meaning the two measurements will be almost always be different.
 
So therefore is it safe to assume that you have the correct CO2 concentration if you have the nice lime green colour despite my PH being 7.2 (KH 5) ?
 
So therefore is it safe to assume that you have the correct CO2 concentration if you have the nice lime green colour despite my PH being 7.2 (KH 5) ?

Only if you have 4dKH water in the drop checker. If you're using tank water for it then it will not give you an accurate measure of the CO2 level as other chemicals will affect the pH reading - it needs to be just (bi)carbonate providing the KH and CO2 providing the acidity to be totally accurate.
 
So therefore is it safe to assume that you have the correct CO2 concentration if you have the nice lime green colour despite my PH being 7.2 (KH 5) ?
No, it's never a safe assumption. The DC is just a test kit and is therefore one-dimensional. Only the plants and fish can tell you what the status is. It can easily be that if your lighting is too high, and/of if your flow distribution is poor, that a green DC means that you do not have enough CO2.

The DC can only corroborate what you see in the tank. It can not determine the results.

Cheers,
 
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