Wide range of CH readings

[jfricker]

I just got my TF100 kit and CH was very high, with these results:
FC 6
CC 0
CH 575 (10 ml test)
TA 90
CYA 70
PH 7.8
I was surprised by the CH and measured it several times. Then I had Leslies measure CH twice on 2 different days with 2 different employees and they got CH = 260 and 270. I had a friend measure with his older TF100 kit with the 25 ml test and he got CH=380. I used my new kit with the 25 ml test and got CH=480. Any ideas on what test to believe?

I do have etching on my plaster that has been getting progressively worse or widespread starting a few years ago shortly after a replaster job. The etching is patches of very rough surface, like 40 or 80 grit sandpaper, and the cleaner picks up sand grain sized pieces of white plaster, maybe I scrape it off when I brush.

I appreciate any feedback.

 

[pooldv]

First, do not believe the pool store. Ever. Review the more detailed test instructions here to make sure you are doing it correctly, Pool School - Extended Test Kit Directions

With numbers like those it seems more likely that you have scale than etching. Those numbers look like they would result in a positive CSI, not a negative one. More about scale and etching here, Pool School - Calcium Scaling

 

[duraleigh]

Trust your own testing....period.

You do not get reassured going to a pool store.

 

[jfricker]

I read the detailed instructions and think I'm doing it right. I retested tonight:
FC = 5
CC = 0
CH = 625
TA = 100
CYA = 50 (not sure what happened here as it's been 70 for all other tests)
pH = 7.8
Poolmath says CSI is .6. The etching spots are shallow pockets in the walls and floor, definitely not protruding scale deposits. The Algae loves to hang on to the rough spots. I've been using bleach for a couple months, no pucks. I guess I'll continue on.