Can you name/identify this pool filter system?

[jdey]

I am an apartment maintenance technician and have been comfortable working on pools until today. I have always worked with DE filter pits with round or rectangular grids. Today I was asked to help with a pool that had a round pit with many, maybe 3/4 or 1/2 inch PVC "spikes" coming up from the bottom. These "spikes" were threaded at the top and capped. Below each cap were 2 small cartridges stacked on top of each other that looked like you would see in an inline water filter for a home faucet. There were tens of these "spikes". I have looked everywhere on line and can't find a thing. I just want a name so I can search for info on how to maintain it. Maybe it's home made or something? Imagine a pit you dig with spikes in the bottom to trap and kill animals... Any help to find info about this would be greatly appreciated!!

[Denniswiseman]

I suggest you post on www.troublefreepool.com with images as you are more likely to get a sensible response there