Finding where the d.e. and debris is getting past can be a challenge as it can be at all the places mentioned above. I have had problems in the past with d.e. filters blowing debris back and eventually replaced every component from the grids to the valve and still had an issue. I'm not familiar with the system 3 with d.e. grids but if you are thinking on changing filters, my opinion is to get a Hayward cartridge filter if you have the bucks. Jacuzzi isn't my favorite filter maker. Either way, you shouldn't have much of an issue replacing filters but you will more than likely have to hard plumb your existing pump to the replacement filter with pvc.