How To Clean A Pool Filter
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Many swimming pool owners do not know how to clean a pool filter cartridge properly. It is very common to hear about pool owners who complain about constantly struggling to keep their pool water clear. After investigating it is discovered that they have not been cleaning the filter cartridges properly, or even worse, they have damaged the filters by using the wrong cleaning method.
A cartridge pool filter is the best overall type of filter in the pool industry. The main downside of them is the cost for replacement cartridges and since the cartridges tend to wear out in three to seven years this is certainly a concern. Sadly, most filter cartridges will never live to be that old because they are not being cleaned properly. Before we get into how to clean a pool filter properly we first should look at what NOT to do.
Pressure washing pool filters - Never pressure wash a cartridge pool filter. While this would seem like the perfect tool for cleaning the gunk out of your filters, the reality is that the paper the filter is made from is simply not strong enough to handle pressure washing. While you may not blast a hole through the paper on your first pass, you can rest assure that you are vastly reducing the service life you will get from them. A cartridge filter is just like paper - high pressure water jets and paper do not mix well. 
Acid washing pool filters
This is another extremely common mistake that pool owners make. Part of the problem is that there is a lot of information online about cleaning pool filters with acid. The problem is not that the acid will ruin the filter, though it is hard on them, the problem is that acid washing will not actually clean the filter so you are left right where you started with dirty filters. Acid washing pool filters is actually something that occasionally filters need however this is a rare situation. If your pool is in a scaling state, and you have a calcium scale buildup on the filters, then acid washing with a very weak solution would be helpful. Having a scaling state in your pool so severe that you need to acid wash your filters would be considered extremely uncommon.
Washing pool filters with a garden hose - Many pool owners will remove their filters and simply spray them off with the garden hose. While this may go a long way towards improving how the filters look, it will not actually improve the flow through them. Rinsing the physical debris off of your pool filters with a hose does almost nothing to actually clean the filter since the paper that the filter is made from is saturated with oil. Water will not remove the oil from the filter.
How Often Should You Clean A Pool Filter
When a pool filter gets dirty you need to clean it to make sure your pool operates normally and the water stay clean and clear...so how often are you supposed to clean a pool filter? While many pool owners will fall into a habit based routine such as cleaning the filters once per season or twice per season, the way you are supposed to clean a cartridge filter is based on pressure.
When you first start up your pool, with newly cleaned filters, you should record the operating pressure that the system is running at. This is one of the main reasons that your pool filter has a pressure gauge on it. Record your this value as this is the "clean operational pressure" for your specific pool installation. If you have a filter gauge with a rotating dial then you can set the green arrow to match with your clean operational pressure. When the pressure in your filter climbs over 7 PSI above your clean operational pressure then this is your sign that it is time to clean the filters. As the filters get saturated with debris, and more importantly oils and grease, then the pressure will rise significantly. In order to remove this oil from your filters you will need to use a chemical product specifically for this application.
How To Clean A Cartridge Filter
So now you know what not to do...so how do you clean a cartridge filter? The main problem is that the filter paper is saturated with oil. You need a chemical degreasing agent to remove this oil. There is absolutely no other way to properly clean a cartridge filter than to soak them in a filter cleaner chemical specifically made for cutting through grease and oil.
overnight. In the morning rinse the filter extremely well with a garden hose. It can be very difficult and time consuming to rinse the filters out properly but take your time with this step to avoid adding filter cleaner back into your pool system. 
instead of a hot tub filter cleaner. Automatic dishwasher detergent is designed to cut through grease and oil without promoting foam or suds which is ideal for pool applications. The only concern with automatic dishwasher detergent would be the presence of phosphates. Phosphates are very bad for swimming pools and you should avoid using a detergent cleaner that has phosphates in it as no amount of rinsing of the filter will fully remove the phosphates. 
