Salt for a SaltWater Chlorine Generator (SWG)
Salt is required with a saltwater chlorine generator (SWG). Salt can also be added to the water to enhance the subjective feel of the water. For an SWG, check the manual for the correct salt level for your unit. This level will typically be around 3,500ppm, but varies with manufacturer.
Salt for Improved Water Feel
For improved water feel without a SWG, try levels around 2,000ppm.
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.
Muriatic Acid in Pool Water Increases Salinity
Every gallon of muriatic acid (31.45%) adds ~36ppm of chloride ions to 10,000 gallons of pool water. Hydrochloric acid is hydrogen chloride or HCl. When hydrogen chloride is added to water, it completely dissociates -
HCl ---> H+ + Cl-
The hydrogen ion adds to the acidity of the water and lowers pH while the chloride ion adds to the measured "salt" level of the water. The K-1766 salt test kit measures chloride ion (Cl-) directly and then reports it's answer in units of NaCl concentration. Your SWG creates sanitizing chlorine from chloride ions.
Salt at Pool Levels Does Not Cause Metal Corrosion
Adding salt to pool water at the levels stated above WILL NOT corrode your pool or damage your pool equipment.
There has been a disturbing trend lately among some pool builders and chemical suppliers to scare people away form saltwater pools by using scare-tactics and fear of pool equipment failure or pool surface degradation. None of these builders or suppliers can back up their claims with actual data and typically use cherry-picked, one-off instances of severe damage which is not necessarily caused by salt.
Salt water in and of itself does not cause metal corrosion. Metal corrosion is entirely dominated by pH and issues with metal corrosion are almost always related to a pool owner not properly keeping their water chemistry balanced.
Over-use of trichlor pucks is one way water can become very acidic and have too low an alkalinity. Salt in water can enhance certain types of corrosion in certain metals (eg, crevice corrosion in aluminum alloys) but the initiation of corrosion is controlled primarily by pH. So don’t be fooled by scare tactics.
Travertine and Limestone Corrosion
Not all travertine is the same, it's quality depend A LOT of where it was mined from and how it was formed. Travertine is nothing more than limestone that has formed from a flowing water source. True travertine comes from hot spring sources where superheated water that is saturated with calcium carbonate rises up to the surface. Once there, the excess dissolved CO2 rapidly outgassed and the pH rises. As the pH rises the calcium carbonate precipitates out of solution. There are two forms of calcium carbonate - calcite and aragonite (different crystalline structures).
If the water that the travertine deposit forms in is hot (the hotter the better), then the aragonite is the preferred precipitate and the travertine will be harder, more dense and less porous. If the water is cooler, then the calcite form is favored where the travertine will be less dense, softer and more porous. In the extreme case of fluvial waters (free flowing cool waters like rivers and lakes), the deposit that is formed is very porous and weak; as such, it is not technically travertine but it is called tufa.
Salt can, in some limited instances, cause accelerated corrosion of certain types of soft limestone, particularly travertine stone and some softer types of flagstone mined in areas of Texas and Oklahoma. These proofs sandstones can allow for the build up of salt inside the microscopic pores of the stones.
If these stones are located in an arid region where precipitation is low and evaporation is high, then the water trapped in these pores will evaporate and the salt that is left behind puts pressure on the pore. Because of the increased pressure from the expanded salt crystal, crack initiation is more likely.
However, this should not deter a pool owner from considering salt water chlorination. Different stone materials can be substituted that are more resistant to salt water OR stone materials can be sealed with a high quality stone sealer.
Stone masons are very familiar with these issues and so, if you are building a pool with natural stone around it, consult with your pool builders stone mason subcontractor to get their opinion on what the best materials are to use in your build.
No Salt for 30 days After New Plaster
One caution with plaster pool surfaces and saltwater pools - when a new plaster surface is applied to a pool, no salt should be added for the first 30 days to allow time for the plaster to cure.
Salt can interfere with the plaster curing process when it is first applied. Salt will often increase the porosity of the plaster surface as well as degrade the calcium carbonate formation process during the curing period.
Wet Edge Technologies Start-Up Guide says adding salt to the finish prior to day 28 may cause spider cracking.
Most plasterers are aware of this issue and will advise you on the proper start up procedure. If your plaster subcontractor has not reviewed startup procedures with you, you can always look at the National Plaster Council (NPC) Swimming Pool Start-up Procedures for details.
Types of Salt to use in Pools
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.
The purer the salt, the better the life and performance of the Chlorine Generator. Use salt that is at least 99.8% pure NaCl, sodium chloride. The preferred and recommended salt is an evaporated, granulated, food quality, non-iodized salt with no additives.
- Avoid using salt with anti-caking agents (sodium ferrocyanide, also known as YPS or yellow prussiate of soda). Filling agents can cause some discoloration of fittings and surface finishes in pool.
- Water conditioning salt pellets are compressed forms of evaporated salt and may be used, but will take longer to dissolve. Such pellets could damage pool plaster and other surfaces in and around the pool.
- Do not use calcium chloride or potassium chloride as a source of salt. (Use sodium chloride only).
- Do not use Rock salt (insoluble impurities mixed with the rock salt can shorten the life of the Cell)
Pool store salt generally costs more and is more finely ground, but even pellets dissolve quickly enough so that isn't really any advantage. Be aware that salt is a naturally mined or harvested (from slat flats) product.
The type of salt sold for pools is not a highly pure chemical grade of salt and therefore will have some impurities in it form the mining process.
If you are doing an SWG pool startup process, then you could be adding hundreds of pounds of salt to your pool. Even if your salt is 99.5% pure, then every 100 lbs of salt added will add 1/2 pound of “impurities”. This can often lead to cloudy water that will take time for your filter to remove. Most of these impurities are just silica dust or other non-toxic compounds.
How long can you store pool salt?
Eons if you keep it dry.
Erroneous salt readings is often the first indication of a failing cell. You should always check your salt level with a salt test kit or test strips before adjusting salt levels.
Salt is measured by different methods in various SWGs. It is normal for salt readings to vary by +/-500ppm between a cell reading and the K-1766 salt test. Refer to the Wiki article for your SWG and How Salt Systems Determine Salinity.
Taylor K-1766 Salt Test
Taylor K-1766 Salt Test Kit instructions
PROCEDURE: CAREFULLY READ AND FOLLOW PRECAUTIONS ON REAGENT LABELS. KEEP REAGENTS AWAY FROM CHILDREN. For 1 drop = 200 ppm Sodium Chloride.
- Rinse and fill the plain graduated cylinder to 10 mL mark with water to be tested.
- Add 1 drop R-0630 Chromate Indicator. Swirl to mix. Sample should turn yellow.
- Add R-0718 Silver Nitrate Reagent dropwise, swirling and counting after each drop, until color changes from yellow to a milky salmon (brick) red. Always hold bottle in vertical position. NOTE: Do not add enough R-0718 Silver Nitrate Reagent to give a brown color. First change from yellow to a milky salmon (brick) red is the endpoint.
- Multiply drops of R-0718 Silver Nitrate Reagent by 200. Record as parts per million (ppm) salt as sodium chloride (salt water).
K-1766 Testing Errors
If the K-1766 sample is staying milky and not turning maroon when expected check you are using a 10ml sample and not 25ml.
Salt Test Strips
Salt Test Strips can be used though they are not as accurate as the K-1766 Salt Test.
Salt Test Meters
There are inexpensive salt test meters that can be used for quick checks of salt level. It is best to use a salt meter along with the K-1766 Salt Test kit and you will see how close your meter is compared to the K-1766 test. If the salt meter indicates a low or high salt problem you should then confirm it with the K-1766 salt test.
Get a salt meter that is calibrated for 3000 ppm of salt. You can find a discussion salt meters on the digital-salt-and-temp-tester thread