CYA Loss

[doloskeeter]

I'm telling myself I've graduated from "Just Getting Started"....to "Testing and Balancing Water"....

I've been using the TF-100 and managing the pool since a renovation in April 2014 (that was the fill date). I just tested the water with the following results:

FC 5.5
CC 0
TC 5.5
PH 7.8
CYA 25
CH 325
ALK 60
Borates - 50

Pool crystal clear

I don't understand why the CYA has dropped When I filled the pool in April, I got it up to 40 and have been chlorinating it to maintain 6 (yes, that is a tad higher than recommended (Chlorine/CYA chart) but I am in Texas and the pool is in full sun all day and I'd rather be safe than sorry (then letting it drop below 3 before I get home from work).

Anyway this morning, I've tested the CYA over and over and it's 25. We have had about 8 inches of rain since April and I've had to drain off about 6 inches since that time and have had to add about 4 inches due to dry spells and evaporation.

I'm nervous that I am over-analyzing that black dot in the CYA test tube, or perhaps have under analyzed it these past few months. I'm scared to add stabilizer because I don't want to jack it up to much so I'm thinking I will put pucks in the chlorinator and just test the CYA daily until it's up to 40.

Can it drop like that?

 

[woodyp]

Suggestion: When you do the cya test, pour the sample back into the red capped bottle then back into the measuring vial a couple of times to get a good "eyeball" check average.

 

[doloskeeter]

Dropping Alkalinity

Trying to keep my threads separate.

Since I have new plaster, I am aware that PH can fluctuate for up to a year. It ranges from 7.2 (after I add acid) and slowly creeps back up to 7.8 -- which is ideal, but it seems like if I let it get to 7.8 and I don't add acid, it is up to 8.2 in a matter of days so I try and add acid when it gets to 7.8.

I don't understand why alkalinity would fluctuate though. My alkalinity is 60 this morning, I think I adjusted it ab out two weeks ago from 60 to 90...so a loss in two weeks. Would substantial rain and subsequent draining of the pool (because water has reached the coping), also affect the alkalinity?

Just curious as to the chemistry of all that.

 

[JasonLion]

CYA does go down very slowly over the course of the season. Between that and the water replacement, it could easily have gone down 5, but 15 seems very unlikely. However, the test is +-15, so you are well within the precision of the test.

 

[doloskeeter]

Thank you. Based on this reply, I'll leave it alone.

 

[Butterfly]

Scroll down to Post #8 the see "Notes" section: http://www.troublefreepool.com/threads/24188-Extended-Test-Kit-Directions

 

[Divin Dave]

Re: Dropping Alkalinity

There are a few reasons why TA might drop, but probably the reason in your case is because of additon of so much MA while maintaining your new plaster.
Adding MA to drop PH also drops TA.

Once your plaster evens out over time, the TA will become more stable as the PH does.

 

[duraleigh]

I have merged your threads. It is really hard for frequent responders to keep up when you have multiple threads going. Keep everything under this one for us.....we'll get you lot's of help!