Thanks for your all of your help. I DO have a skimmer sock. The pump has been running almost 24/7 since Memorial Weekend as I've had to do a lot of water adjusting. Things look great but I guess I should wash out the filter soon. Pressure from return side hasn't changed at all...still seems like a strong flow. The cartridge is a CFR-50 probably about 14" X 16" tall cylinder shaped. Hopefully large enough for an 18' round pool.