Firstly, love this site! I have learned so much and am trying to keep my pool clean personally using PoolMath. I'm trying to replace our filter cartridges. We bought this house with the pool and no background info on any of the equipment. When I look at this old, cracked by heat label, it looks like we have the C4520BH (or C4520LBH) model. However, I'm pretty sure the filters inside are the ones for the C5520BH model. If you look really closely, there seems to be a mark on the box that says C5520BH but the number on the side of the Serial no. box is C4520LBH. The difference between the two filters is their height. The CX875RE (Unicel C-7489) are 25.5" tall while the CX1380RE (Unicel C-7490) are almost 33". Could it be they replaced them with the wrong ones at some point? Would this cause an increase in pressure since I've always noticed this filter runs at 30 psi even with cleaned filters? Any guidance could be a help. I ordered the CX875RE from Amazon and noticed immediately they were shorter than the ones I just cleaned 1 month ago. I can return them but wanted some feedback before I do that and order the others. Thanks in advance!