How to Deep Clean Pool Cartridge Filters - Complete Guide

Tools & Supplies Needed

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First, Let's Diagnose When Your Filter Needs Deep Cleaning

Before jumping into deep cleaning, you need to determine if your cartridge filter actually requires this intensive process. Check your pool system's pressure gauge - when it reads 8-10 PSI higher than your clean filter starting pressure, it's time for cleaning. However, if you're experiencing cloudy water despite normal pressure readings, or if you notice a slimy feel to the filter pleats, your cartridge needs more than a simple rinse.

Look for these signs that indicate deep cleaning is necessary:

• Filter pleats appear discolored (yellow, brown, or gray)
• Calcium scale buildup visible on the filter media
• Oily or greasy residue that won't rinse away
• Filter has been in use for more than 2-4 weeks without deep cleaning
• Pool has experienced algae issues or heavy bather loads

The Complete Deep Cleaning Process

Deep cleaning involves two distinct phases: degreasing to remove oils and organics, followed by acid treatment to eliminate mineral deposits. This two-step approach is crucial because you can't effectively remove calcium scale when oils are present, and vice versa.

Phase 1: Degreasing Treatment

1. Remove the cartridge filter from your pool system and turn off the pump. Always have a spare set of filters so you can maintain filtration while cleaning.
2. Initial rinse with your garden hose using moderate pressure. Spray between the pleats from top to bottom, rotating the filter as you work. This removes loose debris and prepares the surface for chemical treatment.
3. Prepare your degreasing solution using either commercial filter cleaner or trisodium phosphate (TSP). For TSP, mix 1 cup per 5 gallons of water in a large bucket or trash can. Commercial degreasers like Filter Perfect or Kleen It should be mixed according to manufacturer instructions - typically 1 part cleaner to 10 parts water.
4. Soak the filter completely submerged for 8-12 hours or overnight. The alkaline solution will break down body oils, sunscreen, and other organic contaminants that regular rinsing can't remove.
5. Rinse thoroughly after soaking, again spraying between pleats to remove loosened contaminants and all cleaning solution residue.

Phase 2: Acid Treatment for Scale Removal

1. Prepare an acid solution using muriatic acid (hydrochloric acid) mixed 1 part acid to 10 parts water. Always add acid to water, never water to acid to prevent violent reactions. Use a plastic container and wear safety equipment including goggles and gloves.
2. Test the solution by observing if it bubbles when it contacts the filter - this indicates calcium carbonate is dissolving. No bubbling means minimal scale buildup.
3. Soak for 15-30 minutes maximum - longer exposure can damage the filter media. Watch for the bubbling action to subside, which indicates the calcium has been removed.
4. Rinse extensively with fresh water until you can no longer smell chlorine gas (which forms when acid contacts residual chlorine). This step is critical for safety and filter longevity.

Advanced Cleaning Techniques

Pressure Washing Method

If you have access to a pressure washer, use it carefully on the lowest effective setting (typically 1000-1500 PSI). Hold the nozzle at a 45-degree angle about 6 inches from the filter, working systematically through each pleat. Too much pressure or getting too close can damage the polyester media, creating larger pore sizes that reduce filtration effectiveness.

Dishwasher Method for Small Filters

Spa-sized cartridge filters can be cleaned in your dishwasher using regular detergent (no rinse aid). Run a full cycle without heated dry. This method works well for the degreasing phase but should still be followed by acid treatment if scale is present.

Common Troubleshooting Issues

Filter won't come clean: If your filter still appears dirty after deep cleaning, it may have reached the end of its useful life. Cartridge filters typically last 6-12 months with proper maintenance, but heavily used pools may require more frequent replacement.

Shortened time between cleanings: This indicates either inadequate cleaning technique or underlying water chemistry issues. Test and balance your water according to TFP standards - maintain FC levels appropriate for your CYA level, pH between 7.4-7.6, and TA at 80-120 ppm for regular pools.

Filter damage during cleaning: Tears or enlarged pleats usually result from excessive pressure washing or using cleaning solutions that are too concentrated. Replace damaged filters immediately as they won't provide proper filtration.

Maintenance Tips for Longer Filter Life

Implement a rotation system using 2-3 sets of cartridge filters. While one set operates in your pool, the others can dry completely, which helps break down organic matter and makes deep cleaning more effective. Replace filters every 6-12 months regardless of appearance, as the microscopic filtration capability degrades over time even when filters look clean.

Monitor your pool's water chemistry closely - properly balanced water reduces the frequency of deep cleaning needed. High calcium hardness, pH levels above 7.8, or inadequate sanitizer levels all contribute to faster filter contamination.