Can CH be too low?

Howdy Folks,

Thanks for a marvelous forum! I’ve learned more about water chemistry in the last 2 weeks than in a lifetime of messing around with pools and spas. The wealth of knowledge here along with my new TF100 test kit (thanks, Dave) has finally allowed me to see exactly what’s happening and why I’ve had various problems over the years. I am the very definition of “pool stored.” It’s rather embarrassing actually …

Here’s my first set of numbers:

FC = 17 (had just done the superchlorinate thing with the SWG)
CC = 0
PH = 7.8
CYA = 100+ (black dot disappears completely before it gets to the 100 line)
TA = 200
CH = 30 (this area is known for soft water and high alk)

I shocked it because the steps and liner began to feel a little slimy. After 2 days at FC = 17, the slime is gone and FC holds steady over night.

Next I went to work on the CYA. I would have to say that understanding the relationship between CYA and the level of disinfecting chlorine is probably the single most liberating bit of knowledge a pool person can have.

I replaced about 12”of water over the weekend and then I began working on lowering the TA:

FC = 11
CC = 0
PH = 7.2
CYA = 80
TA = 170
CH = 30

I have 2 questions please:

1. Should I do anything about the low CH?

2. What should I do when the Nature2 cartridge expires in the DuoClear? Can I just forget about it or does it need to be removed and the housing capped off in some way? I can probably make a cap from the old cartridge.

Thanks again. This is actually fun now that I understand a little bit about what’s going on.


LifeTime Supporter
Platinum Supporter
TFP Expert
May 7, 2007
Silver Spring, MD
Welcome to TFP!

With a vinyl liner and no spa there is no need for CH, so no need to worry about it being low.

You can always leave an expired cartridge in without a problem. With most models you can remove the cartridge and everything will be fine.
The main reason to keep the CH at around 130 ppm or higher in a vinyl pool is to help prevent foaming. Soft water will foam more readily that hard water if there is any organic load in it.