Size secondary sanitization systems for your pool. Calculate required UV dosage and Ozone output to reduce chemical reliance and kill resistant pathogens. Modern secondary systems provide an additional layer of protection against chlorine-resistant parasites like Cryptosporidium.
Sizing a secondary sanitizer starts with your circulation flow rate, not your pool volume, because UV and ozone treat water only as it passes through the chamber. Enter your pump's actual flow in gallons per minute (GPM) or liters per hour, ideally measured with a flow meter rather than estimated from horsepower. Add your pool volume so the tool can confirm you achieve enough daily turnovers for the system to contact most of the water. For UV, you also specify the target ultraviolet dose, expressed in millijoules per square centimeter (mJ/cm2); pathogen inactivation guidance commonly references 40 mJ/cm2 as a robust benchmark for resistant organisms. For ozone, you enter desired output in grams per hour, which scales with pool size and bather load. Note water temperature and whether the pool is indoor or outdoor, since outdoor pools burn sanitizer faster under sunlight. The most important input is an honest flow rate, because an oversized pump pushes water through the chamber too fast to receive its full dose.
UV dose follows Dose = Intensity × Contact time, so the slower water passes the lamp, the higher the delivered dose. Practically, a UV unit is rated for a maximum GPM at a given dose, so you match the unit's rated flow to your system flow. Worked example: a pool circulating at 50 GPM that turns over 20,000 gallons takes 20,000 ÷ 50 = 400 minutes, about 6.7 hours per turnover, so a 10-hour run gives roughly 1.5 turnovers daily and you select a UV unit rated at or above 50 GPM for your chosen dose. For ozone, a common sizing heuristic is about 0.5 to 1 gram per hour of ozone per 10,000 gallons of pool water, so that same 20,000-gallon pool points toward a 1 to 2 g/hr generator. If your measured flow exceeds the unit's rating, either add a bypass loop to slow chamber flow or step up to a larger unit so every pass receives the intended dose.
Correct sizing matters because an undersized or over-flowed unit gives a false sense of protection while delivering too little dose to inactivate chlorine-resistant pathogens, and an oversized ozone generator can off-gas excess ozone, which is a respiratory irritant that must be vented and properly degassed before water returns to the pool. The biggest conceptual mistake is treating UV or ozone as a chlorine replacement: both work only inside the equipment with zero lasting residual, so you must still maintain a measurable free-chlorine level in the pool body for continuous, whole-water protection between passes. Keep the UV quartz sleeve clean and the lamp within its service life, since scaling and aging quietly cut delivered dose. Never look directly at an energized UV lamp, and follow lockout steps before servicing. After installing a secondary system you can often hold chlorine at the lower end of the safe range, but retest free chlorine, pH, and combined chloramines for a week before settling on a reduced target, adjusting gradually.
UV light destroys the DNA of bacteria and viruses, effectively neutralizing them. It also breaks down irritating chloramines, leading to better air and water quality.
No. Ozone is a powerful oxidizer that works while the pump is running, but it has zero residual. You still need a low level of chlorine to provide continuous sanitization.
Most residential UV bulbs are effective for about 9,000 to 12,000 hours of operation, which typically means replacing them once every one to two seasons.