While a filter-cleaning agent is often recommend to effectively clean buildup on a spa filter, there are other options. A homemade cleaning formula can just as effectively degrease the oils and remove calcium deposits from the filter. And if the filter has excessive amounts of mineral deposits or algae growth, a strong acidic formula is more useful than commercial filter-cleaning products.
Basic Cleaning
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Spa manufacturers recommend cleaning the filter regularly -- as often as every two weeks -- to prevent residue buildup. For a regular cleaning, hosing the filter down with water is sufficient to remove most dirt and other sediment. Spray the filter from the top to the bottom so any dirt flows down. Work between the pleats to dislodge all stuck dirt.
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Oils
Buildup of body oils and suntan lotions on the filter may require a more intensive cleaning. Prepare a solution of 1 cup of trisodium phosphate and 5 gallons of water in a bucket, or mix a solution of 1 cup of dishwashing liquid and 5 gallons of water. Place the filter directly in the bucket and soak it overnight. Rinse the filter well the next day to remove the soap or the chemical. If the filter still has oil on it, soak it again overnight in one of the solutions.
Minerals and Other Buildup
Tackle mineral buildup or a coating of algae on the filter with an acidic solution. Mix 1 part muriatic acid with 6 parts water. Be sure to add the acid to the water, not the water to the acid, as splashing acid can cause severe burns. Soak the filter in the acid until it stops bubbling. Rinse the filter thoroughly to remove all traces of the acid.
Tips and Warnings
Do not use diatomaceous earth to clean a filter cartridge; the powder may become trapped in the filter and damage it or make it less effective. If any oils or mineral deposits remain on the filter, it may restrict the water flow through the filter and prevent it from working effectively. Ensure that the filter is completely clean before reinstalling it in the spa. Always wear gloves and eye protection when handling muriatic acid.