Don't know. Koi are happy, growing and healthy. Tested the GH a few days ago and it was way over 200. I've got to get some decent test kits for GH and KH. Maybe I'm underestimating their importance but I'm beleive with all my oyster shells (like the Japanese use them) I should be ok. Why is kh so important? It should be a seperate thread..we are hijacking this one.