" Using LSI - Langelier Saturation Index "
Article by: Jeff Bogdanof of Vineyard Pools in Clovis, California
What does balanced water do ?
1. Keeps water "in solution" = Prevents water's damaging properties from affecting your pool to both extremes - corrosive or alkaline.
2. Prevents scale (alkaline) = Known as the rough deposits that build up and make the tile, and pool plaster painful and even clog plumbing.
3. Prevents corrosive water = Prematurely eating away your plaster/pebble, delicate insides of your heater, and costing repairs of other items.
4. Helps ensure your pool finish warranty is not voided. At Vineyard Pools we exclusively use "Wet Edge" pool finishes in installations.
a. Plaster - 3 year warranty (9 good years with balanced water)
b. Altima stone - 7 year warranty (40% quartz finish, 60% plaster finish, with stronger concrete additives)
c. Luna Quartz - 7 year warranty (100% quartz finish)
d. Satin/Pearl Matrix pebble pool finish - 15 year warranty - Recommended finish in almost every application by Vineyard Pools
LSI helps tell you 3 things about your pool water overall:
"Is my pool water corrosive, balanced, or alkaline (opposite of corrosive) after you input all the following measured elements?
Key levels to monitor to keep your water balanced:
1. Alkalinity 80 - 120 ppm ideal
2. Calcium Hardness 200 - 400 ppm ideal in pools (150 - 350 ppm ideal in hot water spas)
3. Cyanuric Acid 40 - 70 ppm (over 100 ppm you are encouraged to drain your pool to dillute the CYA level)
4. Temperature Use the Pentair Pools LSI calculator and input farenheit. Technically it would be a "temperature factor" but the calculator makes this part simpler.
5. pH 7.5 is ideal. Range of 7.2 to 7.8 is somewhat acceptable
6. Salt water pool - Salt water pools have close to 3500 ppm of salt. A salt water pool's salt can make the water slightly more corrosive overall. "Yes/ No" option in calculator
* Vineyard Pools recommends reliable liquid drop testing when measuring pool water. Test strips are not reliable standards to use in our professional opinion.
After inputing your measurements into the calculator, your OVERALL water hardness/softness will be explained with a number. "zero" would be the best number because it means your water is balanced taking all 6 factors into account that deal with the saturation index.
If LSI Index is between -0.3 and +0.3 pool water is Balanced.
When pool water is balanced, it has no effect on the pool or equipment. There are two values you can readily change to help improve your LSI value to get it into the optimum range: pH and Alkalinity level.
If LSI Index is less than -0.3 pool water is Corrosive.
Pool water may cause etching, pitting, dissolving and staining of walls, grouting and plumbing.
- As Cyanuric acid stabilizer Increases, LSI Decreases
- As Total Dissolved Solids Increase, LSI Decreases
To raise your LSI value, add sodium bicarbonate or baking soda (can be found in pool supply stores). Consult the calculator to determine the target Alkalinity value (recommended range is 80-120ppm; however, you may find that a level lower than 80 may be ideal for a balanced LSI value).
If LSI Index is greater than +0.3 pool water is Scale Forming.
Pool water may deposit excess minerals on the pool and equipment. Scale generally appears as white or lightly colored rough blotches on the pool walls. It also adheres to other objects in the pool, piping and filter system. Scale can restrict water flow, shortening filter runs and reducing filtration efficiency.
- As Temperature Increases LSI Increases
- As Total Alkalinity Increases LSI Increases
- As pH Increases, LSI Increases
- As Calcium Hardness Increases, LSI Increases
To lower your LSI value, add muriatic acid (can be found in pool supply stores). Consult the calculator to determine the target pH value (range is 7.2 to 7.7)
More in Depth Explaination of each element below from the LSI for those who want to know more :)
TA - Total Alkalinity - "Father" to pH - controls and keeps pH maintained
Total alkalinity indicates the water's ability to buffer pH changes. Buffering means you need to use a larger quantity of a chemical to change the pH. At low TA levels, the pH tends to swing around wildly. At high TA levels, the pH tends to drift up. TA contributes to the CSI which indicates the tendency for plaster damage or calcium scaling.
The ideal TA level depends on several factors. If you are using acidic chlorine sources, such as trichlor or dichlor, keep TA on the high side, perhaps between 100 and 120. If you have a SWG, or if you commonly run water features such as a spa, waterfall, or fountain, keep TA on the low side, between 60 and 80. Otherwise levels between 70 and 90 are good. Pools with plaster surfaces should factor their CSI into the preferred TA level decision. Pools with vinyl liners can tolerate high TA levels reasonably well.
You can raise TA with baking soda. It is often best to make large TA adjustments in a couple of steps, testing the water after each one, as adding baking soda will also affect the pH and you don't want the pH going out of range. If you need to lower your TA level, see How To Lower Total Alkalinity.
pH - Acidity/Alkalinity - "Son" to alkalninty
pH indicates how acidic or basic the water is. pH should be tested daily at first. Once you gain experience with your pool, less frequent monitoring may be appropriate, depending on your pool's typical rate of pH change. pH levels between 7.5 and 7.8 are ideal, while levels between 7.2 and 7.8 are acceptable for swimming.
pH levels below 7.2 tend to make eyes sting or burn. pH below 6.8 can cause damage to metal parts, particularly pool heaters with copper heat exchange coils. High pH can lead to calcium scaling. pH contributes to the CSI, which indicates the tendency for plaster damage or calcium scaling. Aeration will tend to cause the pH to rise. This can be mitigated by lowering TA.
Many pools will drift up towards higher pH over time. This is particularly true for fresh plaster (particularly in the first month and continuing for perhaps a year) or when TA is high and the water is being aerated (because of a spa, waterfall, fountain, SWG, rain, kids splashing in the pool, etc).
You can raise pH with borax or soda ash/washing soda. Soda ash/washing soda will increase TA more than borax will. You can lower pH with muriatic acid or dry acid. How much you will need for a given pH change depends on several other numbers, most importantly your TA and borate levels. Higher TA and/or borate levels cause you to need larger amounts of chemicals to change the pH.
CH - Calcium Hardness
Calcium hardness is primarily the topic. But Total Hardness covers all mineral salts in the water, such as calcium (75% of total hardness) can also be indicates the amount of calcium in the water. Over time, water with low calcium levels will tend to dissolve calcium out of plaster, pebble, tile, stone, concrete, and to some extent fiberglass surfaces. You can prevent this from happening by keeping the water saturated with calcium. In a vinyl lined pool there is no need for calcium, though high levels can still cause problems. A plaster pool should have CH levels between 250 and 350 if possible. Calcium helps fiberglass pools resist staining and cobalt spotting. If you have a spa you might want to keep CH at at least 100 to 150 to reduce foaming. CH contributes to the CSI which indicates the tendency for plaster damage or calcium scaling.
You increase CH with calcium chloride, sold as a deicer and by pool stores, or calcium chloride dihydrate, sold by pools stores for increasing calcium. You lower calcium by replacing water or using a reverse osmosis water treatment.
TH - Total Hardness
Total hardness is the sum of calcium hardness and magnesium hardness. 75% of TH is calcium, so calcium and TH can be used interchangeably.
CYA - Cyanuric Acid
Cyanuric acid, often called stabilizer or conditioner, both protects Free Chlorine from sunlight and lowers the effective strength of the FC (by holding some of the FC in reserve). The higher your CYA level, the more FC you need to use to get the same effect. It is important to know your CYA level so you can figure out what FC level to aim for. If you don't have a Salt Chlorine Generator or you have problems from extremely high amounts of sunlight, CYA is typically kept between 40 and 70 ppm. If you have a chlorine generator or very high levels of direct sunlight, CYA is typically kept a little higher. However, 100 ppm many professionals recommend dillution of the pool water. Some also have allowed levels up to 200ppm being tolerable and requiring drainage above that level. Ideally keep it lower than 100, if it's higher, keep your eye out for issues such as the often disputed "chlorine lock".
You increase CYA by adding cyanuric acid, often sold as stabilizer or conditioner. CYA is available as a solid and as a liquid. The liquid costs a lot more, and generally isn't worth the extra expense. Solid stabilizer can take up to a week to fully register on the test, so don't retest your CYA level for a week after adding some. Solid stabilizer is best added by placing it in a sock in the skimmer basket. The pump should be run for 24 hours after adding solid stabilizer and you should avoid backwashing/cleaning the filter for a week.
In nearly all cases the best way to lower CYA is to do a partial or majority drain and refill the water. It cannot be chemically removed or taken out of the water unless in some circumstances you have a high degree of bacteria in your pool that literally eats the CYA and will proceed to poop nitrates. In that case, your pool is in a bad condition and draining is still a likely solution if not other complex problem.