Bob Lowry Breaks Down the Most Powerful Chlorine for Pools

 Chlorine gets marketed with big numbers, and those numbers often create more confusion than clarity. Pool owners and even many pros hear that liquid chlorine is “weak” because it might say 10% or 12.5%, while trichlor tablets can claim 90% or 99% available chlorine. The key is learning what those percentages actually describe and how they’re measured. Some labels reflect weight-to-weight concentration, others use trade percent conventions, and liquids introduce volume-based assumptions that don’t map cleanly onto dry products. A practical comparison cuts through the noise: a gallon of 12.5% sodium hypochlorite delivers about one pound of pure chlorine equivalent, while a pound of trichlor delivers roughly 0.9 pounds of chlorine equivalent. Once you translate products into “pounds of available chlorine delivered,” the strongest chlorine type becomes a math question, not a branding contest, and you can dose accurately for pool sanitation and water chemistry control.  

A big reason “available chlorine” feels strange is the historical standard used to define it. The industry compares products to chlorine gas as the baseline, assigning it a value of 100% available chlorine. But chlorine gas is Cl2, and when it reacts in water, it forms hypochlorous acid (HOCl), the primary active sanitizer, and hydrochloric acid (HCl). In simple terms, part of the molecule becomes the disinfecting form and part becomes acid, yet the comparison system still treats chlorine gas as the 100% reference point. That convention forces other products to be expressed relative to that standard, which is why trichlor can be labeled around 90% available chlorine even though a strict molecular accounting would suggest a lower “chlorine-only” fraction. Understanding this helps you interpret chlorine strength, active chlorine claims, and why “more percent” on the bucket does not automatically mean “more chlorine delivered to your pool today.”  

No matter which sanitizer you choose, every chlorine source adds something besides chlorine, and that byproduct shapes long-term water balance. Liquid chlorine adds sodium and, after use, effectively leaves behind salt. Cal hypo adds calcium, which can raise calcium hardness and increase scale risk if pH and saturation index climb. Dichlor and trichlor add cyanuric acid (stabilizer), which protects chlorine from UV loss but can accumulate and reduce chlorine effectiveness if it gets too high. These side effects matter for troubleshooting algae, cloudy water, scaling, and chronic chemical demand. Choosing the “best” chlorine is often about controlling what else comes with it, aligning with your pool surface, local fill water, and maintenance style, and preventing runaway buildup of cyanuric acid, calcium, or salt over a season.  

Salt water chlorine generators deserve special clarity because they are widely misunderstood. A salt system is a chlorine-producing device: it uses dissolved salt to generate chlorine gas in the cell, which immediately dissolves and forms hypochlorous acid in the water. It also produces sodium hydroxide and hydrogen gas, which explains why salt pools commonly experience rising pH. The hydrogen bubbles and cell turbulence increase aeration, accelerating carbon dioxide off-gassing and pushing pH upward even further, so acid management becomes a normal part of salt pool care. Output is also limited: many systems top out around one pound of chlorine per day at 100% over 24 hours, and real-world performance depends on proper salt level and, critically, proper voltage and current to the cell. If the control system or power supply under-delivers current, chlorine production drops and the pool can’t keep up, even when the generator is running nonstop.  

Salt also changes the environment around the pool in ways owners don’t expect. In the water, the salt concentration is far below ocean water and is often compared to the salinity of tears, so swimming comfort is usually fine. The problem shows up when splashed water evaporates on decks, rails, stone, and metal. Evaporation leaves salt behind at full strength on the surface, which can accelerate corrosion and damage finishes. That connects to another crucial topic: bonding and grounding. Because salt water conducts electricity better, poor bonding can increase the risk of electrolysis and corrosion issues throughout the equipment pad and pool structure. Proper bonding ties metal components and equipment together with a common conductor and appropriate grounding, reducing stray voltage behavior in what is effectively a large low-voltage electrical environment. Finally, a common operational mistake is thinking a generator’s boost mode equals shocking the pool. Boost simply increases output over time; it cannot raise free chlorine fast enough for urgent superchlorination. When you need a true shock level quickly, liquid chlorine or cal hypo is the practical solution to raise free chlorine immediately.