Keeping Stains and Scale from Coming Back

            So you just got the stains off your pool and it's looking great! But you're worried it's not going to last; as soon as you add something else to the water you're afraid that the stains will come right back.

            Often when you're finished with a stain removal procedure, you have to re-balance the water - whether it means bringing your sanitizer levels back up or adjusting your pH. This is also when you are most likely to drop the stains back out, since you are affecting the solubility of metals with these adjustments. So how do you re-balance AND keep stains off the pool? Here are a few tips to do just that:

            Tip 1: Lower you Total Alkalinity


            Lowering the Total Alkalinity as little as 10ppm can make a huge difference. Ultimately, you have to experiment; lowering Total Alkalinity and see how long it takes for the stains to return. Eventually, you'll hit an Alkalinity that keeps the stains away.

            Odds are you are using the Langelier Saturation Index (LSI) which recommends a Total Alkalinity of 80-120ppm. Unfortunately, this is typically too high for most pools. Total Alkalinity measures carbonates, and carbonates + metals = stains. Therefore, the higher your hardness, the lower your Total Alkalinity needs to be.

            However, as hardness builds up the lower the Total Alkalinity will need to be maintained. You can refer to our Hamilton Index article to get a more precise target values, and a deeper explanation of the chemistry. To give you an idea, a Calcium Hardness level of around 100 ppm would mean a Total Alkalinity of just under 100 ppm. However, a Calcium Hardness level of 1500 ppm would need a Total Alkalinity of 40ppm.

            Tip 2: Test in a Bucket Before Adding


            Get a bucket of pool water, and add a little bit of the intended chemical to see if there is a reaction. If the water turns a clear emerald color, that's from metals coming out of solution. Odds are if you add more, you'll have metals fall out that will stain. If you see stains appear in the bucket, they're likely to form in the pool.
            Wouldn't be great to find out if something is likely to stain BEFORE adding it to the pool? Using a bucket of pool water to test is your best bet. While there's no guarantee that you won't get a stain, it's usually a good indicator. Odds are you're going to put in a higher concentration of the chemical in the bucket, so a reaction has a higher probability. If it looks good, you can pour the bucket in the pool, which brings us to our next tip:


            Tip 3: Predissolve Everything


            Instead of adding a chemical directly into the pool, make a slurry of the chemical in a bucket of water before pouring it into the pool. This will reduce the chance of things settling to the bottom and leaving a stain.
            The higher the concentration, the more chemical energy a reaction can have. This means adding something straight to the water can cause a temporary high concentration, leading to a reaction that might force metals out of the water leading to staining. Predissolving chemical in a bucket of water will not only lower it's initial concentration, but help it dissipate into the water faster.
            Updated: 01 Aug 2017 06:10 AM
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