For all of you who suffer with the Intex cartridges, there is a solution.
Firstly you need to get some replacement filters made of a different material called Reemay.
This is a spun polyester and is the same as used in 'proper' filters.
You will need at least 2, one to use and the other to swap when cleaning.
I am on my second season with mine and they show no sign of deterioration or loss of filtering ability.
They are available online from here and probably from other outlets as well:
Intex A replacement:
http://www.filtersfast.com/Filbur-FC-37 ... Filter.asp
Intex B replacement:
http://www.filtersfast.com/P-Intex-Pool ... Filter.asp
Now for the cleaning. This is a simple, cheap, safe and effective method which won't damage your filter.
You will need:
Garden hose with a spray nozzle (don't use a pressure washer), bucket, pack of clothes whitener containing only Sodium Percarbonate available from the laundry powder section in any supermarket.
Please note that different brands contain different concentrations often with little or no difference in price so check. I use one which contains 35%.
1. Remove filter and flush out housing. Insert your clean 2nd filter.
2. Spray wash filter with spray nozzle on garden hose. Turn upside down as you spray.
3. Place about 1/4 to 1/3 cup of whitener in bucket. Place filter in bucket. Fill bucket with hot water, dunking and turning the filter up and down as it fills with water.
4. Leave to soak overnight.
5. Remove filter and repeat step 2,
6. Leave on counter to dry.
Note: Always wash filter immediately without allowing it to dry out before cleaning.
Steps 2 to 5 may need to be repeated for very dirty filters, but usually not.
I tested dishwasher powder of good quality and it hardly worked at all, so stick with the above whitener.
Pic showing before and after: