20 mrt 2026
Swimming pool water filtration with ozone: filtration systems and ozone treatment combined
A pool filtration installation and an ozone system work together as components of one water treatment process, but each fulfils a different function. The mechanical filter removes suspended particles and solid impurities from the water by passing it through a filter medium. The ozone system addresses the dissolved organic load: dissolved ozone reacts with organic compounds that are not retained by the filter medium and chemically breaks them down through oxidation. The sequence of both processes in the water treatment chain is relevant. Water that is first mechanically filtered before reaching the ozone system contains less suspended material that unnecessarily lowers the ozone concentration by reacting with those suspended particles. That sequence optimises the effectiveness of the ozone treatment. The filter types commonly used for private swimming pools are sand filters, cartridge filters and DE filters. Each filter type has its own filtration grade, its own maintenance profile and its own suitability for combination with an ozone system. The choice of filter type and the sizing of the filter installation influence the effectiveness of the ozone treatment, because an undersized filter supplies the ozone treatment with more suspended material than necessary. This article describes the relationship between mechanical filtration and ozone treatment in pool water treatment.
Swimming pool water filtration with ozone: how mechanical filtration and ozone treatment work together, filter types and the optimal sequence in the water treatment chain.
Pool filtration and ozone: cooperation, sequence and filter types
Two functions in one water treatment chain
Pool water treatment typically consists of two complementary processes: mechanical filtration and chemical treatment. The mechanical filter removes suspended particles and solid impurities. The ozone system treats the dissolved organic load through oxidation. Both processes address a different type of contamination and complement each other in the water treatment chain. More on the ozone system and available equipment: ozone water machine.
The combination of filtration and ozone treatment gives a water treatment process that addresses both suspended and dissolved organic load in the pool water. A filter without ozone treatment allows dissolved organic compounds through. An ozone system without prior mechanical filtration is burdened with suspended material that unnecessarily consumes ozone. The combination of both processes in the correct sequence gives the most efficient water treatment.
The optimal sequence: filter before ozone
The sequence of filtration and ozone treatment in the circulation line is relevant to the effectiveness of the ozone system. Water that is first mechanically filtered before reaching the ozone system contains less suspended material. Suspended material consumes dissolved ozone because the ozone also reacts with those particles. A lower level of suspended material at the inlet of the ozone system means that more ozone is available for reaction with the dissolved organic compounds in the pool water.
The recommended installation sequence is therefore filter before ozone in the circulation line. Water is led via the circulation pump through the filter, then through the ozone system, and then returns to the pool. That sequence maximises the effectiveness of the ozone treatment at a given ozone production capacity. More on how ozone works in pool water: ozone treatment swimming pool water.
Filter types and filtration grade
The common filter types for private swimming pools are sand filters, cartridge filters and diatomaceous earth filters. A sand filter uses quartz sand as filter medium and retains particles above approximately twenty-five micrometres. Sand filters are durable and require little maintenance beyond periodic backwashing. A cartridge filter uses a membrane and retains particles above approximately ten micrometres. A diatomaceous earth filter retains particles down to approximately five micrometres and gives the finest filtration grade of the three types.
A finer filtration grade lowers the level of suspended material in the filtered water and thereby increases the efficiency of the ozone treatment. For pools where the effectiveness of the ozone system should be as high as possible, a filter with a finer filtration grade is a worthwhile choice. The choice of filter type should be matched to the pool volume, the maintenance effort the owner is willing to provide and the desired filtration grade for the combination with the ozone system.
Sizing the filter installation
The sizing of the filter installation is a basic technical requirement for the effectiveness of the total water treatment system. An undersized filter processes the pool water insufficiently quickly to keep up with the total organic load. The flow rate through the filter system expressed in cubic metres per hour must be matched to the pool volume and the desired water turnover time. A common recommendation is that the total pool volume passes completely through the filter system at least once every eight hours.
The pump circulating water through the filter and ozone system must have sufficient capacity for the combined hydraulic resistance of filter and ozone system at the desired flow rate. Too low a pump capacity results in too low a flow rate and thereby insufficient treatment of the total pool volume per unit of time. More on the ozone system: ozonewater.
Filter maintenance and its effect on ozone efficiency
A saturated filter with a high dirt load has reduced filter performance and higher hydraulic resistance. Regular backwashing of a sand filter or replacing a cartridge filter element maintains filter performance. The frequency of maintenance depends on the usage intensity of the pool, the environment and the amount of organic material reaching the pool via swimmers and the surroundings.
A well-maintained filter subjects the ozone system to less suspended material. A poorly maintained filter with a high dirt load passes more suspended material to the ozone system, resulting in higher unproductive ozone consumption and a lower effective ozone dosage for the dissolved organic compounds in the water. Filter maintenance therefore directly influences the effectiveness of the ozone system. More on pool surface cleaning: swimming pool cleaning ozone water.
Contact time and ozone concentration in the system
The contact time of the ozone with the water to be treated in the ozone system is a determining factor for the effectiveness of the oxidation reaction. Longer contact time at sufficient ozone concentration gives a more effective oxidation reaction on dissolved organic compounds. Contact time in pool applications is determined by the ratio between the flow rate of the water through the ozone system and the internal volume of the contact reservoir or contact pipe.
A correctly sized combination of filter installation and ozone system with a matched flow rate gives a water treatment process that efficiently combines mechanical and chemical purification of the pool water. The two-cloth method for surface cleaning of the rim and terrace around the pool connects to this water treatment approach: two-cloth method.
Ozone and algae control via filtration
Algae in pool water are organic compounds that react to ozone oxidation. The oxidation reaction of dissolved ozone with the organic structures of algae contributes to reducing the algae concentration in the water. After the oxidation reaction the broken-down algae fragments are present as solid particles in the water. The mechanical filter then removes those broken-down particles from the water. The combination of ozone oxidation and mechanical filtration thus works together in controlling algae in pool water. More on algae control: algae swimming pool ozone water.
Ozone, filtration and algae control together
Algae in pool water are organic compounds that react to ozone oxidation. The oxidation reaction of dissolved ozone with the organic structures of algae contributes to reducing the algae concentration. After the oxidation reaction the broken-down algae fragments are present as solid particles in the water. The mechanical filter then removes those broken-down particles. The combination of ozone oxidation and mechanical filtration therefore works together in algae control. A well-maintained filter with sufficient filtration capacity and an effective ozone system give the best result when addressing algae growth in pool water.
Seasonal maintenance of filter and ozone system
The organic load of the pool water and thereby also the load on the filter system and the ozone system varies seasonally. During peak season with intensive use and higher temperatures the maintenance needs of both the filter and the ozone system are higher than in the shoulder seasons. An adapted maintenance routine with higher filter backwashing frequency and regular checking of ozone production during peak season keeps the system in optimal condition. At the start of the swimming season a thorough check of both systems is a worthwhile step to begin the season well.
Pressure drop and system monitoring
The pressure drop across the filter gives a direct indication of the dirt load of the filter medium. Higher resistance in the filter at equal pump setting results in a lower flow rate through the system. Pressure gauges at the inlet and outlet of the filter measure this pressure difference. When the pressure difference exceeds a threshold value backwashing or replacement of the filter medium is indicated. Regular reading of pressure gauge values is a simple but effective method for preventive filter management.
Circulation pump and system balance
The circulation pump forms the engine of the water treatment chain. The pump must have sufficient capacity for the combined hydraulic resistance of filter and ozone system at the desired flow rate. Too low a pump speed results in insufficient flow through the ozone system and thereby too short a contact time for the oxidation reaction. Too high a pump speed can shorten the contact time in the ozone system and reduce the filtration grade. The correct pump setting is therefore a determining factor for the effectiveness of both systems. More on the ozone water installation: ozonewater.
Water temperature and system performance
Water temperature influences the effectiveness of both filtration systems and ozone treatment. At higher water temperatures the solubility of ozone is lower resulting in a lower maximum achievable ozone concentration at equal production capacity. At lower water temperatures the viscosity of water is higher leading to higher hydraulic resistance in the filter and correspondingly higher energy costs for the circulation pump. Knowledge of the temperature dependencies of both systems helps with interpreting measurement results and adjusting system settings over the course of the season.
Costs and affordability
The total investment in a combined filter and ozone system for pool water treatment should be weighed against the expected savings on chemical consumption and improved water quality over the lifetime of the installation. A correctly sized combination of filter installation and ozone system gives water treatment performance that is not achieved with chemical treatment alone. Questions about the application? get in touch.
Testimonials
💬 "After we correctly adjusted both the filter and the ozone system, the water quality of our pool became more stable. We notice that the filter reaches saturation less quickly than before." — Private pool owner
Further reading
Full overview: ozone water knowledge guide. Ozone versus chlorine in pools: ozone swimming pool vs chlorine. Algae control in pool water: algae swimming pool ozone water.