How Do You Remove Stains Due To Calcium Hardness Being Too Low?

by MJM
(Dallas Texas)

While we were away a Good Samaritan neighbor turned the water on into our pool to replace evaporation loss but forgot to turn it off again. The pool overflowed and flooded the yard (almost 1/3 acre).

The result was the same as if we had emptied and refilled the pool. The CYA (which had been high) went to zero and the pool turned green. We have corrected all that, but did not realize that the Calcium Hardness had also dropped.

The pool started to get dark stained looking areas and the Polaris leaf bag started to have what seemed like grains of sand in it. I am afraid that the plaster has been etched from the pool in many places. I added some Calcium Chloride this evening but wonder if there is any way to remove the stained areas. I hope it is not too late for that.

The most recent reading for the pool (before adding the calcium chloride today) are as follows:
Chlorine 2
CH 150
CYA 60
TA 90
pH 7.6

More details:

DE filter
25,000 gallon gunite pool that was here long before we bought the house 7 years ago.
Polaris pool cleaner that we had been running 12 hrs/day but recently changed to 6 hrs/day.
Location: Dallas TX

Last Friday it was 105 F but it is in the 80s this week.

For chlorination we have been using the 3" stabilized chlorine tablets in floaters and shocking the pool with Leslie's power powder plus which I think is calcium hypochlorite. The last time I added chlorine it was regular 8.25% liquid chlorine bleach.

I have been told that eventually a gunite pool will need to be re-plastered but we lived in our previous home 15 years with no plaster problems and the pool had been there for a long time before that.

My main questions are:

1. Am I doing the right thing by adding Calcium Chloride? (The guy at Leslie's told me I didn't have to but I am sick about the condition of the plaster and suspect it is due to the low CH)

2. Is there anything I can do to remove the dark stains on the steps, sides and bottom of the pool? The water itself is crystal clear and sparkling.

I will take a sample of pool water back to
Leslie's tomorrow to see what the chemical levels look like after adding the CaCl. I have installed a 'Sentry' pool leveler to automatically add water to the pool to compensate for evaporation loses.

Thank you for your help. The online advice is a godsend!

Thanks for the question

I'm not aware that low calcium can cause staining. Normally low CH with plaster pools will result in pitting which means the water will pull the calcium carbonate out of the plaster, weaken it, and cause pitting.

CH levels for plaster pools should be 150 - 250ppm. This will more than satisfy the water's need for hardness. If your fill water hardness is already high, over 150ppm or so, there's no need to add calcium chloride, or if there is a need, very little.

You first need to determine the kind of stain you have, either organic or metal staining. A couple very simple tests will do it.

Get a chlorine tab or a sock filled with 1/2 lb. of granular chlorine and place it on a stain. If the stain fades it's organic and you'll need to shock.

If the stain doesn't fade or gets darker, get some crushed up ascorbic acid (Vitamin C tabs) and put that in a sock on a stain. If the stain lifts a bit, it's a metal stain and you'll need to do an ascorbic acid treatment.

If you know you're fill water has no metals, the staining is probably organic but I'd encourage you to do the ascorbic acid test just to confirm and rule everything out so you're not wasting money and chemicals.

You can find the ascorbic acid treatment in this link.

Your readings seem to be right in line. The CYA is just a bit high. Normal range is 30 - 50ppm but just keep an eye on it. By using Trichlor tabs you're slowly increasing the CYA. For every 10ppm of chlorine added with Trichlor tabs you'll raise the CYA by 6ppm.

Do these tests then get back to me with the results and we can go from there.

If you would like personal assistance, I do phone consultations for a donation of your choice. It makes things go much faster. If you choose to not go that route, we can correspond by email.

Contact Me


Hope this helps.


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Calcium Gardner For Scale Build Up

by Linda Le Grand

I have an 18,0000 gallon fiberglass pool that has scale build up. I had my pool company come out to give me advice on how to remove it. He recommended Calcium Hardner and or Scaletec. Could not find the hardner anywhere so I bought scaletec.

I have used approx 4 gallons of Scaletec over that past 3 months but then water temps dropped and I was told it would not work in cold water. He said to use the calcium hardner starting with pump off and add2 gallons and let it sit for 30 minutes them scrub with a soft stainless steel brush. Since I could not find the calcium hardner I used Scaletec in the same fashion. I would say it helped about 40% but scrubbing did not touch it,most just sluffed off and I vacuumed it daily.

My question is does Calcium Hardner remove the scale and is it safe for my fiberglass pool? Also, should I scrub it. He also said they could block the pool drain it and wet sand then repolish the surface if needed. Pretty expensive.

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