How quick does etching occur?

sdrilling

Member
Nov 20, 2018
14
Newnan, GA
We purchased our home with an older Pebbletec pool in October. In the past couple of months I have made several posts on TFP as we resolved some of the problems. After discharging the pool company and taking our pool chemistry in hand (and after spending days reading the most excellent discussion on TFP about chemistry) we have beautifully clear pool water with an SI within +/- .3

Question: When I look in the deep end and in a few places elsewhere I see what appears to be etching. The pool is the cleanest it has been since we purchased it so it "might" have been there before it is hard to tell. Also, we had a quarter size white rough spot in the shallow end when we first purchased the pool. Now I see 5 or 6 more.

How quickly does etching form? Basically nothing was done to correct the pool chemistry for 2 months. Does it occur this quickly or does it take months/years to form?




Background

Today Readings
PH 7.3
TA 120
CH 250
CYA 65 (down from 160+)
Chlorine - holding at 5 for past two weeks. -- We had to use breakpoint chlorination to resolve the zero that existed since October or earlier. It took 25 PPM to break out.

The pool maintenance guys partially drained the pool 24000/34000 ish gallons last week in November. They came back to re-fill it on December 4th. When they found the CYA was still above 90 they recommended we drain the pool completely and pay $2000 for them to acid wash. They informed us that would be the only way for us to get our pool chemistry right. After checking with TFP we declined. They never showed back up so I guess they cut us loose.

9/5 J&M Maint Pre Purchase Inspection TA 70, CH 230, PH 7.0 (Using Taylor Test Kit)
10/5 Browns TA 41, CH 274, PH 7.7
11/1 J&M Maint TA 90, CH 300, PH 7.2
11/13 J&M Maint TA 100, CH 160, PH 7.4
11/20 J&M Maint TA 100, CH 407, PH 7.2
11/20 Browns Pool TA 40, CH ? PH 7.2
11/28 Pool partially drained. Upper portion of the pool sat dry for 3 days waiting for pool maint to come back.
12/4 Pool refilled
12/5 - Browns Pool TA 0, CH 2 PH 7.3
12/18 - Opulent Pool TA 31, CH 230, PH 7.5
1/17 - Owner Taylor Kit TA 71, CH 168, PH 7.9 Before we made all of our adjustments to correct
1/30 Owner Taylor Kit TA 110, CH 230, PH 7.6
 

Arizonarob

Gold Supporter
Silver Supporter
TFP Guide
Mar 25, 2018
2,548
Chandler Arizona
If your CYA is 70 (always round up to the next level) then you need to be a min of 5ppm, but your target should be 7-9ppm FC.
See the chart here... CYA/FC Chart

Also you said...
The pool maintenance guys partially drained the pool 24000/34000 ish gallons last week in November. They came back to re-fill it on December 4th. When they found the CYA was still above 90 they recommended we drain the pool completely
If they drained 34k gallons from your pool, then according to your sig line, your pool is 34k gallons, it would have been empty. Even at the minimum of 24k gallons, 3/4 of your water would have been gone. Are you sure on those numbers?

I’ll ping a couple of people to help you with the rest. :cheers:
@JamesW @JoyfulNoise @ajw22
 
Last edited:

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
20,489
Laughlin, NV
Etching, or plaster degradation, takes some time. And none of your tests you show, if anywhere near correct, horribly low pH or any indicator of a severe environment for the plaster.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
6,802
Northern NJ
Your pool is what it is. It is impossible to say why something happened with an incomplete picture. What will speculation accomplish?

Maintain your pool following TFPC methods and you will be fine going forward. Please use PoolMath and post a complete set of tests from your TF-100 including water temp and CSI.

Have you reviewed ABCs of Pool Water Chemistry and read Pool School?