There are five chemical levels that every pool owner needs to keep track of:
FC – Free Chlorine - A sanitizer which keeps your pool water safe and free of germs. Chlorine must be constantly replenished. (# depends on CYA)
pH – Acidity/Alkalinity - Needs to be kept in balance to prevent irritation and protect the pool equipment. (7.2 to 7.8)
TA – Total Alkalinity - Appropriate levels help keep the pH in balance.
CH – Calcium Hardness – Appropriate levels help prevent plaster damage. High levels can cause calcium scaling on all pools.
CYA – Cyanuric Acid - Protects chlorine from sunlight and determines the required FC level. In the state of Louisiana, levels should be in the range of: (10-30)
FC – Free Chlorine Free chlorine shows the level of disinfecting chlorine available to keep your pool sanitary. Normally, FC should be tested and chlorine added daily(through a chlorine feeder or floater. FC is consumed by sunlight, and by breaking down organic material in your pool. The level of FC you need to maintain depends on your CYA level and how much you use the pool.
It is important that you do not allow FC to get too low, or you run the risk of getting algae. If FC ever gets down to zero, or you have algae, the pool is not safe to swim in. Maintaining an appropriate FC level is the most important part ofkeeping your water in balance.
It is most efficient to raise the FC level in the evening, since none will be lost to sunlight until the next morning. FC normally goes down by itself. If you must lower the FC level quickly, you can use a chlorine neutralizer (sodium thiosulfate).
TC – Total Chlorine Total chlorine is the sum of FC plus CC (combined chlorine). Inexpensive chlorine tests, such as a 7 way test strip, which shows the TC level. In normal operation, TC can be used as if it was FC, because CC is usually zero.
pH – Acidity/Alkalinity 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.
Many pools will drift up towards higher pH over time. This is particularly true for fresh plaster, 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.
TA – Total Alkalinity 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 (pH bounce). 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.
CH – Calcium Hardness Calcium hardness 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 orcalcium 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. Most test strips report TH instead of CH. The ratio of calcium to magnesium varies. As an approximation you can multiply TH by two thirds to get a rough estimate of CH.
CYA – Cyanuric Acid Cyanuric acid, often called stabilizer or conditioner, both protects FC 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 SWG or problems from extremely high amounts of sunlight, CYA is typically kept between 30 and 50. If you have a SWG or very high levels of direct sunlight, CYA is typically kept between 70 and 80. If you are using an ORP controller, keep CYA below 50, in the state of Louisiana CYA levels should be between 10-30.
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.