I just bought the 24' version of this pool, so I can provide some information.

First off the built in clorinator it is refering to is a joke. Basicly the filters that they sell have a hollow middle and they recommend you put 1 inch clorine tablets in there. It in no way produces clorine.

The included filter is the bare minium and very noisy. You will have to run it a lot longer than a stronger filter to get any results and have to watch your water carefully. My orignial plan was to use the filter until it broke and then upgrade. I have multiple years of frame pool experience and after one month I have already decide this filter is not worth running. The included filter system could not filter the dirt from the bottom of my pool. It would pass through the filter system right back to the bottom of my pool. Nothing ticks me off more than to vacuum the bottom of the pool and see a trail of dirt coming out of the filter system.

You can connect a different filter to the outlet of the existing hole exit with clamps. You will have to play a bit with hose sizes depending on what filter you upgrade to.