I recall reading something on this forum from Vaughn that mentioned using a known KH sample and pH liquid to find out how much CO2 is in the tank. I have a Red Sea CO2 indicator in my tank. The only problem is I have no idea what green means in terms of how many ppm CO2 is in the tank? Anybody have any idea what green means translates ti in terms of ppm for the Red Sea CO2 indicator?

DIY Drop Checker - Aquatic Plant Central- aquascaping...a living art should answer the question. You need to make your own KH standard water, using distilled or DI water so you are sure there is nothing else in that water that affects the acidity or alkalinity except for the CO2. The Red Sea indicator water will have the same ppm of CO2 in it as the tank water has, and you can measure the ppm in the indicator because you know that water is "perfect" for doing so.

The liquid that comes with the red sea kit? Any idea what it is? Is it pH liquid?

I'm pretty certain it is just pH reagent, the same as is used in pH test kits. The amount you add to the bulb is not critical so just add enough to get an easy to see color.

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 !!!
=============

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 !

Interesting results.

How do you create the perfect KH=4.0 solution? Use distilled water and then what?

Baking powder (sodium bicarbonate).

The KH reference notion is Vaughn's idea and it's application to the visual drop checker, not mine.

I'd thought of a pH version with an air gap, but quickly realized some problems with that and switched to a membrane pH probe seperator.

Vaughn, you need to consider a larger thin version of the drop checker without any air gap, just the reference solution seperated via the membrane.

That would greatly enhance the response time.
More surface area and thin(but enough depth for decent color resolution), just a snap box that you could fill the KH ref solution into and seal with the membrane to the tank water.

Sort of like those SeaChem NH4 thingys folks use.
Humm.......I suppose I could call Greg Morin and tell him.

Seems like a good idea.

Al, I think they believe most NO3 issues are from fish, thus the production of HNO3, nitric acid which can mess with things.

Regards,
Tom Barr

How does one really dial the solution to KH=4 though? Get a large sample of DI water, approximate the sodium bicarbonate needed to dial in the solution to KH=4, and then use a KH test kit to see how close you are?

The way I used to zero in on a 4 or 5dKH distilled water solution was to start with about a cup of distilled water. Add a very tiny amount of baking soda. Then test a sample with a 4X size sample - I use a narrow bowl wine glass to make it easier to see the color. With the AP test kit, one drop normally equals one dKH, but with 4X sample size one drop equals .25 dKH. If you have supreme good luck your water is found to be at the KH you want. If not, it will almost certainly be too high. Guess at how much more distilled water is needed to dilute it down to the KH you want and add that. Do another test. When you repeat this a few times you get the KH you want, and if you really want better accuracy then, use 10X sample size for the last KH test. I had great luck making 4 dKH water, but lousy luck making 5 dKH water. I ended up with 6 dKH, and mixed half and half with 4 dKH to finally get it at 5 dKH.