need advice on staining

[Guest]

I'm new here, and would appreciate your expert advice!
I have a 9 year old plaster pool, and with our basic knowledge, we have never had an issue. We try to keep the water balanced and have not had any problems. Until now.
I backwashed last week, and the autofill kicked in. That night I shocked the pool. The next day I woke up to what looked like dirt in the pool. Since we are in Az and in the desert, it's not unusual for a dust storm to move in and leave a mess behind! So, my first thought was that it was dirt - it was a light tan, streaky in places, mottled looking in places. But when the cleaner didn't pick it up, and the brush didn't move it, I knew it was something else. My local pool guys (that seriously have never steered me wrong), told me to shock again, with massive doses of shock, so now my chlorine is completely off the chart. Anyway, when that did nothing, I took them some more pics - and this time he told me to use "Pool Stain Treat" by United Chemical. He said it was scale. As my PH was on the high of normal, he told me to lower ph first, but I did not need to be concerned by the chlorine, and could use the stain treat without lowering the chlorine. Of course, as soon as I added the acid to the pool, I read the directions for the "Pool Stain Treat" and saw that the Stain Treat would also lower acid - which of course it did. So, it was in the pool overnight, and I don't see any difference in the staining,(hubby says it's lighter, I'm not sure),but PH is really low, chlorine really high. Here are some questions:
1. How long do I need to wait to know if this is going to work? (husband says it's lighter, but I'm not sure)
2. My PH is now too low (in the 6's), do I need to bring this up immediately, or will low PH help remove the scale?
3. Any other advice you can give me?

 

[JasonLion]

There are a couple of possibilities. The two most likely are iron stains and calcium scaling.

Try putting a vitamin C tablet on one of the stained areas and see if that has any effect. If it is iron staining the vitamin C should clear up the stain right where the tablet is placed.

If it is scaling, something as simple as what the pool store suggested is very unlikely to work and has some risks of it's own. Leaving the PH that low can help remove scaling, but it can also remove plaster from places you don't want plaster removed from. It is best not to attempt low PH procedures without a lot more preparation than you have done. I suggest raising the PH to at least 7.0 right away.

It would be a huge help if you could post a complete set of water test results. That will help us narrow down what might be happening and advise you more specifically about what to try next.

 

[Guest]

Vitamin C did not seem to do anything.
I will get the PH up, and post test results.

 

[Guest]

I just test the PH and the total alkalinity - can you tell me the best way to raise PH with total alkalinity this high?
PH is about 6.8 and TA is at 100.

 

[maxepr1]

Aeration will lower your TA at that PH level.

 

[Guest]

I have added some 20 Mule Team and am running the aerator - in just a few hours my PH has raised to 7.2 - I feel comfortable with this level.
The pool people tell me that it will take a week to see if the Stain Treat is going to work, and for the scale to break down, or start to break down.
Still high chlorine - I haven't tested everything else, but will do so later.