Where did my KH go?

[WhiteCloud]

I got my Pressurized CO2 system...brought my pH down from 7.8 to 7.2 in over a few days.

My KH as always been 6 since I have been testing it (6 months). Today I tested my KH to make sure my CO2 was in the proper range..and it has dropped to 4? GH remains constant at 6.

Any idea how the KH just drops like that? Is that normal? Should I worry about increasing my KH somehow to maintain buffering capability? Should I drop my pH a little more (like to 6.9 ot 6.8) to keep my CO2 between 15-20 ppm?

I am going to attempt to test for CO2...but I find the Red Sea test I have very difficult to read...and I usally see no color change with that test as I have a pretty bad case of color blindness...prehaps I can get my wife to help.

Thanks,

WC

 

[BASSNMAN]

Your plants use up the compounds that make up kh. 1 teaspoon of sodium bicarbonate will raise 50 l about 4 degrees without raising total hardness.

 

[betowess]

As I noted in the other post, many folks with pressurized CO2 tanks keep some calcium carbonate in the cannister filter to maintain depleted KH from CO2 injection. Every few months you have to replace it. Maybe half to 3/4 cup of crushed coral, oyster shells or the like... for a bigger 90 gallon tank. I use oyster shells cause I like to eat oysters and the CC is free.
Also, you could just use the Chuck Gadd chart which easily tells you the dissolved CO2 concentration in a tank by comparing KH to pH ratio. There is a link in the other post.

And pH of 6.7 to 6.8 would be great for the plants, though obviously one should consider what fish you want to keep as well. HTH.

 

[BrianNY]

I also think the reagent for the KH test doesn't last forever. I took some readings with one that I had for a little more than a year and it registered 1. I was suspicious because the pH was quite stable. Bought a new KH test and the reading was in fact 6.

 

[BONESTOCK]

Hmmm...interesting Brian. Was there an expiration date? Maybe we should bring this up to the companies. :?