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Pool Water balancing is not such a complicated exercise. It is simply the relationship between different chemical measurements in your pool water. Your pool water is constantly changing, year round. Everything that comes into your pool will affect your pool water balance - in short, anything that comes in contact with your pool water.
You will probably not change the water in your pool for many years. Continuous filtration and disinfection removes contaminants which keep the water enjoyable but this is does not balance your water. A pool that is "balanced" has proper levels of pH, Total Alkalinity, and Calcium Hardness. These are: pH: 7.2-7.8, Total Alkalinity: 80-120 ppm, Calcium Hardness, 180-220 ppm and Cyanuric Acid (Stabilizer): 30-50 ppm. Chlorine levels should remain constant in the 1-3 ppm range.
It may also be defined as water that is neither corrosive or scaling. This concept of water balance is derived from the fact that water will dissolve and hold minerals until it becomes saturated and cannot hold any more water in solution. It reminds me of the school science experiment, where you dissolve spoonful after spoonful of salt (or sugar) in a beaker, until at last - the water will dissolve no more salt into solution, and the grains just sit on the bottom of the beaker.
When water is considerably less than saturated it is said to be in a corrosive or aggressive condition. When water is over saturated and can no longer hold the minerals in solution it is in a scaling condition. So then, balanced water is that which is neither over or under-saturated.
The cliché that "water seeks its own level" certainly applies here. Water which is under-saturated will attempt to saturate itself by dissolving everything in contact with it in order to build up its mineral content. Water which is over-saturated will attempt to throw off some of its content by precipitating minerals out of solution in the form of scale. How do we know when our water is over or under saturated?
Buy a good test kit (with fresh testing reagents) to measure the chemical levels of pH, alkalinity, and calcium hardness. Being able to accurately test cyanuric acid, free and total chlorine and acid and base demand is also important. To run complete home pool water analysis, use the same test kit the pool stores use, the Taylor K-2005, or the same test kit as health inspectors, the ColorQ Pro.
Any good discussion on pool water balance would certainly cover some definitions on pH, Total Alkalinity and Calcium Hardness levels in pools.
pH is a measure of how acidic or basic the water is. pH is a logarithmic scale from 0-14, with 7 being neutral. Below 7.0 and a substance is defined as being acidic, while levels above 7 are said to be basic or alkaline. Everything that enters your pool has a pH value. Ever heard of acid rain? This is rainfall with a very low pH. The human eye has a pH value of 7.35, being just slightly basic. This is, coincidentally, in range with proper pH levels for your pool. To have pH in balance we adjust the water with additions of pH increasers (bases) or pH decreasers (acids) to achieve the range of 7.2 - 7.6, or more precisely, 7.4. Keep both on hand (pH Up/Down), to be able to make complete adjustments when needed.
If your testing (recommended daily) of the water shows a pH value below 7.0; the water is in a corrosive (acidic) condition and you will need to add a base to bring the pH into a more basic range to prevent corrosion. It doesn't take too long for a low pH condition to weaken vinyl, strip heat exchangers and erode plaster. Conversely, if the pH is above 7.8, the water is in a scaling (basic) condition and must add an acid to bring down the pH to prevent the formation of scale or calcium deposits on our tile, in the filter, or even precipitation out of solution into a cloudy water condition. Another effect of high pH is that chlorine becomes less active, almost sluggish. At a pH of 8.0, only about 20% of your chlorine is available to kill pathogens and contaminants.
A close cousin of pH, the level of alkalinity in the water is a measurement of all carbonates, bicarbonates, hydroxides, and other alkaline substances found in the pool water. pH is alkaline dependent; that is, alkalinity is defined as the ability of the water to resist changes in pH. Also known as the buffering capacity of the water, alkalinity keeps the pH from "bouncing" all over the place. Low alkalinity is raised by the addition of an Alkalinity Increaser, to prevent pH drift. High levels of alkalinity are lowered by the addition of an acid (pH Decreaser), to allow adjustment of pH, up or down.
We recommend "pooling" the acid in a small area of low current for a greater effect on alkalinity. That is, adding an acid underwater, in a deep end corner with the pump off, creates a greater hydrocarbon exchange for a greater effect on lowering TA in your pool. Acids will lower both pH and alkalinity, but “walking the acid” around the pool in a highly distributed manner is said to have a greater effect on lowering the pH than the alkalinity. Pooling the acid has the opposite effect. So then, to lower pH ‘walk your acid’, and to lower alkalinity ‘pool your acid’.
A very important component of water balance, alkalinity is usually best in the 80-120 ppm range, but in some cases can be run outside of this range with little problem. Levels should be tested weekly. Follow package label for treatment guidelines.
You can’t reduce total alkalinity levels without also pummeling your pH level, because the same chemical (Liquid Acid or Dry Acid) is used to lower both pH and Alkalinity in pools. Pooling your pH decreaser in one calm and still area of the pool (or in an attached spa) increases hydrocarbon exchange resulting in a greater reduction in Alkalinity levels, as opposed to walking your pH decreaser, or pouring it around the edge of the pool.
How much alkalinity increaser to add to your pool depends on your pool size and current tested level of total alkalinity; adding 1.25 lb. of Total Alkalinity Increaser, per 10,000 gals, will raise pool alkalinity by approximately 10 ppm.
When we speak of scale, we are talking about calcium carbonate which has come out of solution and deposited itself on surfaces. It is a combination of carbonate ions, a part of total alkalinity and calcium, and a part of the Calcium Hardness level. The test for Calcium Hardness is a measure of how "hard" or "soft" the water is. Hard water can have high levels of calcium and magnesium. If these levels are too high, the water becomes saturated and will throw off excess particles out of solution which then seek to deposit themselves on almost any surface inside the pool. They can be attracted to ladders, lights and in extreme deposit themselves as very small crystalline clumps, patches or film - all over the pool surfaces. Calcium Carbonate scale is a white-ish, crystal that mixes with other contaminants.
If the Calcium Hardness levels are too low, the water is under-saturated. If under-saturated, the water will become aggressive as it attempts to obtain the calcium it needs. Such "soft-water" will actually corrode surfaces inside the pool which contain calcium (like pool plaster) and other minerals to maintain its hardness demand.
If your Calcium Hardness levels are too high you can use a product called CalTreat to correct, with varying levels of success. In most cases you need not worry if your calcium levels are below 500, but much higher than that and it can cause pool problems. Hardness can also be reduced by dilution (adding water to the pool which has a lower calcium hardness content). Levels which are too low require the addition of calcium chloride. Recommended range for calcium hardness is 180-220 ppm, or some say 200-400 ppm. Calcium Hardness test can be done weekly with hardness test strips.
Also called the Langelier Index, this chemical equation or formula is used to diagnose the water balance in aquatic environments (pools). The formula is "SI = pH + TF + CF + AF - 12.1".
To calculate the Saturation Index, test the water for pH, temperature, calcium hardness, and total alkalinity. Refer to a chart for assigned values for your temperature, hardness, and alkalinity readings then add these to your pH value. Subtract 12.1, which is the constant value assigned to Total Dissolved Solids and a resultant number will be produced. A result between -0.3 and +0.3 is said to indicate balanced water. Results outside of these parameters require adjustment to one or more chemical components to achieve balance.
This formula is not guaranteed; however, some readings for pH, calcium, and alkalinity which, if taken individually would be considered to be well beyond recommendations, can combine within the formula to produce "balanced water". The SI can be used to pinpoint potential water balance problems, and the water’s propensity for precipitation or the chance of corrosion. Pentair has a nice Saturation Index Calculator that is easy to use, no slide rule needed.
These are important measurements of your water cleanliness, but have nothing to do with water balance, but more with sanitation. A chlorine test should be done daily, or as needed, to maintain a 1-3 ppm level at all times, depending on your level of cyanuric acid, or stabilizer. Higher cyanuric acid levels will require higher chlorine levels, because cyanuric acid has a suppressive effect on the activity of free chlorine.
Cyanuric acid levels fluctuate much less than chlorine, test for stabilizer monthly, to maintain a 20-40 ppm range. Cyanuric acid levels above 50 ppm should be reduced by dilution; that is, draining a portion of pool water and refilling with unstabilized water, or you can use Bio-Active CYA Remover, with varying levels of success. If filling a pool add enough cyanuric acid to raise to 20 ppm, or 2 lbs per 10000 gals, and stabilized chlorine tablets will add more from there.
Total Chlorine is the sum of Free Chlorine and Combined Chlorine, aka Chloramines. DPD test kits and some test strips test for both Free and Total chlorine, any difference between the two being attributed to combined chlorine. If the sample darkens noticeably, or there is a measureable amount of combined chlorine, greater than 0.3 ppm, a good pool shock is in order, to break apart chloramine molecules. Chloramines are no longer active sanitizers, impart a strong chlorine odor and cause swimmer ‘red-eye’, and get in the way of free chlorine trying to do its job. Test your pool weekly for chloramines with a DPD Kit or use ShockChek test strips.