What type of filter is generally considered least effective in a swimming pool?

The cartridge filter is typically considered the least effective among the options provided for swimming pool filtration. This type of filter utilizes a pleated element that captures debris and particles as water flows through it. While it can remove larger particles and provide decent filtration, its effectiveness diminishes when dealing with very fine contaminants.

The reason cartridge filters are seen as less effective compared to sand filters, diatomaceous earth (DE) filters, and activated carbon filters lies in their filtration capacity. Sand filters can trap larger debris and, with proper backwashing, maintain effectiveness over time. DE filters excel in removing very fine particles due to their fine filtration capabilities and can filter out particles as small as 3 to 5 microns. Activated carbon filters are great for removing organic substances and improving water clarity, odor, and taste.

In contrast, the cartridge filter's design limits its ability to handle finer particles efficiently, making it less effective overall for comprehensive pool sanitation compared to the other types of filters. Hence, it is often perceived as a less robust choice for achieving optimal water quality in swimming pools.