I've just tried the method with the 4dKH reference solution and it looks to be working really well ...
What I've also decided to try were a couple of other CO2 test methods to compare results.
I had an old Red Sea CO2 test kit and tested the water with this....
I also checked my PH and KH and put this through the usual charts ....
A neighbour have me an old JBL permanent test kit, this is now also in the tank (tank water + reagent) ...
The results:
Drop checker with KH4 solution/bright green colour = 30ppm
Red Sea Co2 kit (liquid reagent type) = 64ppm !!!
PH/KH PH=7.0 Kh=13 CO2=39ppm
JBL permanent test kit = Co2 between 24 - 36ppm
=====EDIT=====
The fish and shrimp in my tank are all doing fine, no signs of stress from high CO2 levels ...... So i'm fairly sure the Red Sea kit's reading of 64ppm is way off the mark !!!
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The only one of the above methods that does NOT rely on tank water is the one that VaughnH and Tom have discussed on here.
I dont add any PH/KH adjusting/buffering agents, the substrate is ADA Aquasoil (known to impact on PH & KH) and the ferts are ADA ferts (brighty K & Step2), but this tank will be running EI as from next week.
Interestingly the JBL kit says it can measure Co2 only if "there are no other substances in the water which lower PH (e.g peat, PH-lowering agents,
Nitrate).
Does
NitrAte influence the reading of PH/KH/Co2 tests ?
I'm also checking the water using the method of looking for a drop of 1 PH in degassed water. I'll look at this tomorrow, my normal tap PH is about 7.8.
Cheers
Al
P.S. I've mentioned this reference KH solution method over on the planted tank section of
Tropica Fish Fourms, Hope thats OK, I gave due credit for all the hard work done by VaughnH & Tom on this method. Just wanted to spread the word a bit !