CYA - Cyanuric Acid
Cyanuric acid, often called stabilizer or sometimes conditioner, both protects FC from sunlight and lowers the effective strength of the FC. The higher your CYA level, the more FC you need 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 60 and 80. If you are using an ORP controller, keep CYA below 50.
You increase CYA by adding stabilizer. Solid stabilizer can take up to a week to dissolve, so don't retest your CYA level for a week after adding some. You can add stabilizer to the skimmer, in which case you must not backwash or clean the filter for the next week. You can also put stabilizer in a sock and hang the sock near a return. The only practical way to lower CYA is to replace water.
Borates can be used to control pH drift due to a SWG or high aeration levels. Borates also help to control algae. Various subjective water quality/feel improvements are also attributed to borates. If you are not intentionally using borates there is no need to test for them. To use borates to control pH rise and algae, add borates to between 30 to 50 ppm. With borate levels at 30 or above there is a chance that pets which drink the majority of their water from the pool might have some problems. Since pets should always be trained to not drink pool water, this shouldn't be a problem.
You increase borates by adding borax and acid, or by adding boric acid. 20 Mule Team Borax can be found in the laundry detergent section of most large grocery stores. Boric acid is available over the Internet. You lower borates by replacing water. Proteam's Supreme, Bioguard's Optimizer Plus, Omni's Maximizer, and Poolife's Endure all contain borates.
Suggested FC Levels
You need to adjust your FC target level based on your current CYA reading. Higher CYA levels bind up more of the FC, requiring higher FC levels to get the same disinfecting chlorine level. Many people find that a SWG will work with a slightly lower FC level than other forms of chlorine. The normal FC target is given as a range because different pools require different FC levels. If your water starts looking dull or just slightly cloudy try using a higher FC target.
The target FC level is a minimum. You always want the FC level to be at least as high as the target level. FC is commonly lowest in the evening after sunlight has been reducing it all day. If you are adding chlorine once a day in the evening you need to bring the chlorine up to a higher number than this so that your FC level the next evening is at least the target level. How much higher depends on your CYA level, the amount of sunlight that falls on the pool, and how much the pool is used. A CYA of 30 to 50 will generally lose between one half and two thirds of the FC over the course of a sunny day.
Shocking your pool means bringing the FC level up to high levels and holding it there. This will kill anything that might be living in your water and to speed the breakdown of CC. If you have mustard algae you often need to shock at a higher FC level than usual to get rid of the mustard algae. You may also need to move towards the high end of the normal FC range to keep the mustard algae away.
Be careful if your CYA level is really and truly zero. When CYA is really zero you should not bring the FC level above 5. If you have ever used stabilizer or dichlor or trichlor your CYA level won't really be zero. CYA levels up to 15 or 20 can sometimes test as zero. The suggested FC level feature treats a CYA of zero as if it was really one or two.
Salt is required with a SWG. Salt can also be added to the water to enhance the subjective feel of the water. For a SWG, check the manual for the correct salt level for your unit. This level will typically around 3,000, but different models vary. For improved water feel, try levels around 2,000. These levels are less then one tenth of the salt level in ocean water, which has around 35,000 ppm of salt. People vary in their ability to taste low levels of salt. A few people can taste salt levels as low as 1,000, others not until 3,500 or more.
Having salt in the water just slightly increases the risk of corrosion, particularly to surfaces that water splashes onto where the water can evaporate, leaving high concentrations of salt behind. This is normally only a problem for stone work above the water line made from softer kinds of stone. There is a lack of solid information about the salt corrosion risks for many materials, leading to debate about the overall level of risk. Most people with salt in their water do not experience any problems.
Salt can be added using solar salt, sold for use in water softeners (sodium chloride). You want the kind that is 99.4% pure or better and which doesn't have any rust inhibitor or other additives. Crystals are fine. Pellets will work but dissolve slightly more slowly. Pool store salt generally costs more and is more finely ground, but even pellets dissolve quickly enough so that isn't really any advantage. Potassium chloride can be used but you will need 17% more of it and it costs more.
CSI - Calcite Saturation Index
The calcite saturation index is a tool for estimating the likelihood of plaster corrosion or calcite scaling. The LSI, Langelier Saturation Index, is a very similar but slightly less accurate measure. The CSI uses pH, TA, CH, CYA, temperature, Borate, and Salt levels to estimate the likelihood of problems. A low saturation index means the water is likely to dissolve calcite out of plaster, pebble, tile, stone, and concrete surfaces (and perhaps fiberglass) which will eventually cause damage. A high saturation index means the water is likely to deposit calcite scale on the walls of the pool and in the plumbing.
CSI is most sensitive to changes in pH. With a plaster pool, it is best to try and get your CSI a little below zero, so that changes in pH won't shift your pool too far towards corrosion or scaling. With a vinyl pool the CSI can be kept more negative, which makes it very unlikely that pH changes could get the CSI into the range of scaling risk.
Suggested Goal Levels
The Pool Calculator can display suggested goal levels from either traditional sources, or from TroubleFreePool.com. Select the source you would like to use and also your primary source of chlorine and pool surface. Suggested goal levels will be displayed for FC, pH, TA, CH, and CYA. Suggested goals are simply a starting point. There are many situations that are not covered by these basic guidelines.
Bleach - Liquid Chlorine
Common bleach sold in grocery stores is the same thing as liquid chlorine or liquid shock sold by pool stores in some states. You want bleach without any additives, typically labeled unscented or "original scent". Check the strength of the bleach when comparing prices. Bleach with a higher percentages of sodium hypochlorite is more effective and easier to carry.
ORP - Oxidation Reduction Potential
A kind of sensor that reacts to disinfecting chlorine levels which is used in some systems that automatically feed chlorine into the pool based on the sensor's measurement of the current chlorine level in the pool.