Discoloration in a plaster pool further discolored

[HappyWino]

I'll cut to the chase first and add detail if needed

I applied some ascorbic acid (in the form of crushed Vit C tablets) to a couple of discolored areas in my pool (the discoloration is over most of it but this was just a test). The areas that were treated all took on a grey discoloration that disappeared (along with the original stain) when I added chlorine (superchlorination).

The conclusion I have drawn is that yes, the discoloration is metal based but what I am not sure about is whether the grey discoloration was just a result of me not having a sequestering agent in there to suspend the released metals and if it was, why did chlorine appear to remove it?

Any insight is greatly appreciated.

Thanks

HW

 

[JasonLion]

As a general rule ascorbic acid removes metal stains and chlorine removes organic stains. It is possible that you have a mixture of both metal and organic staining, though it is usually one or the other. Failing to add sequesterant just means that the stains will come back more or less the same when the PH goes up, it wouldn't cause some third color to appear.

 

[DavidD]

Jason is right about the removal of the different types of stains by using the ascorbic acid and chlorine so I guess it is possible you have a combination of both. The thing that gets me is that you say the chlorine removed the grey but didn't bring back the original stain however it does take time and they could have been re-deposited elsewhere.

Happy, post some test results for FC, CC, pH CYA, Alk and CH as well as what type (Gunite/plaster, Vinyl, Fiberglass etc.) of pool you have.

Dave

 

[HappyWino]

Hi David,

This is a 15k gal. gunite/plaster pool and the discoloration has been there since we moved into the house about 4 years ago (I _think_ it has become worse but I couldn't swear to that)

FC: 14 (pretty much zero when I add the tablets)
CC: 0
PH: 7.6
CYA: 50
TA: 130
CH: 300 (I think)

The vitamin C tablets I used were white and 100% ascorbic acid according to the label. The grey stain was worse than the original stain, I was pretty relieved when it disappeared after adding chlorine but I want to know what is going on before going large scale :|

 

[HappyWino]

I went ahead with the ascorbic acid stain treatment and added 4lbs of acid 2lbs at a time with two days in between (pool stats in the first post). PH was about 7.2 when I started and seems to have remained fairly steady. The first application did improve things but not as much as I had hope so I went with the second treatment. Since the second application the pool has been cloudy white. TA is testing at 90, PH is still around 7.2 and I added a gallon of chlorine yesterday evening (the acid was added Tuesday evening).

Any suggestions what is causing the cloudyness and should I be concerned?

Thanks

 

[JasonLion]

The cloudiness could be from many different things. If you are following the full treatment you will have been keeping your chlorine down while lifting the stain. In that case it is probably algae. It is common to get some algae when doing the acsorbic acid treatment. There isn't much to be done until you can bring your chlorine levels up again.

 

[HappyWino]

Doesn't "feel" like algae

I forgot to mention that I did put 5oz of 60% polyquat in the week before, and the week of treatment, as a preventative measure for this. The cloudiness was present before I added any chlorine and was white not green (or any other algae color).

I have had algae outbreaks in the past and they have always been green and started on the steps and sides. This time there isn't anything visible on the steps or sides, just this overall cloudyness, I can't see the bottom in the deep (6.5ft) end at all.

What are the other possibilities? Could the lower than usual PH have caused "something" to drop out of solution in the water? Could this be calcium being leached out of the plaster? Could it be that I need more chelating agent in there to tie everything up?

Thanks

 

[JasonLion]

It could be calcium. Calcium will sometimes come out of solution when the PH goes up. Bleach will raise the PH temporarily, it goes back down as the chlorine gets used up. Based on your old test numbers I wouldn't suspect calcium. The acorbic acid treatment would have taken a little calcium out of the plaster, but not normally enough to matter or to get cloudiness given you initial numbers.

There are dozens of things that can cause cloudiness. See Ben's chart of 100 reasons for a cloudy pool.

Can you get us a full set of new numbers?

 

[HappyWino]

I'll pull some numbers tonight and post them...

As for the "100 reasons..." thats a long list I think the cloudiness is definitely related to the treatment, it showed up within hours not gradually over days.

I just realized I omited one thing, about an hour before adding the second batch of acid I added 8-10oz of dry acid to try and drop the PH a little more (didn't move appreciably)

 

[Guest]

Certain copper stains can form a grey to black stain that is very difficult to remove from plaster. I suspect it was not the chlorine that removed them but the low pH over time. What color was the original staining? Clouding of the water is normal when you are removing stains with a reducing agent like ascorbic acid and a metal sequsterant. It usually clears in a few days. The pump should run continuously during this period.