Calcium Hardness Question?


LifeTime Supporter
TFP Expert
In The Industry
May 20, 2007
SWSuburban Chicago, IL
Using my temporary HTH 6-way test from Wal-mart....

The Calcium Hardness test says "add 5 drops and water should turn RED" - BUT my water turns pink. :?

I added 46 drops to turn it purple-blue, which means my calcium (for my vinyl AG pool) is 460? But the pool store's last 4 tests ranged from a low of 70 to a high of 173.

I have not added any calcium or Calc-Hypo to the pool since the 173 reading.

Can I assume that since the water turned pink and not "red" the 460 reading is not accurate? Any thoughts?

My water is clear and my chlorine seems to be holding, just using bleach these days.... :)

CL 5+
ph 7.2
TA 150
CYA 80

The Mermaid Queen

LifeTime Supporter
TFP Expert
Mar 28, 2007
Northern KY
Since you have a vinyl pool, CH is an irrelavent measurement. If it gets really high, over 500, and you have a high TA, you can get cloudy water...

The only way your CH could go up is if your fill water has a Calcium content of over 173 (assuming the 173 was accurate)

I have never seen the HTH test, so cannot advise you on this. I would just say don't worry about it, and when you get the TF-100 test kit you can recheck accurately!

chem geek

LifeTime Supporter
TFP Expert
Mar 28, 2007
San Rafael, CA USA
Metal in the water can interfere with the Calcium Hardness (CH) test. Try adding some drops of the titrant (the drops you count) first to the water sample and include those drops in your total count. Then add the calcium buffer and indicator and then the titrant drops (starting from the count of drops you've already added at the beginning). See if that helps.

You can also try testing your tap water to see how that works -- that will tell you if your test kit is any good. You can also dilute your pool sample with an equal part of filtered or bottled water and then double the count of drops (or ppm reading).

I assume you are using the 25 ml sample size where each drop counts as 10 ppm as opposed to the 10 ml sample size where each drop counts as 25 ppm.


LifeTime Supporter
Jun 6, 2007
Doylestown, PA
The test kit I purchased from Ben (PS233) does the same thing for CH. Turns pink, then changes to purple. No red or blue about it. All of the other tests seem to work as directed.

Adding 5 drops of the titrant first helped - but it was still a reddish-pink to a blueish-purple change. Same readings though. Also, it does the same thing with my tap water.