We are pool owners by default- it happened to come with our house when we bought it from the bank. We aren't quite sure what we're doing!
We bought a new filter 2 years ago and had a new liner put in this year. After the new liner went in and the pool was filled with water we did not open it right away, we put the cover on and let it sit for a few weeks. After the trees finished flowering we opened the pool. It was just about black! We put the filter together and turned it on and within a day it was crystal clear albeit in need of a good vacuum. Since that time we had a new baby, so a few weeks went by without vacuuming. Then when we got ready to vacuum we noticed that the pressure was going up on the filter, it would go down when we backwash but goes right back up shortly after. The return water coming out of the eyeballs is strong right after backwashing but weakens very shortly after. The skimmers have very little suction, we are not able to vacuum on filter mode, only on backwash mode and it's wasting water as well as overflowing our backwash well.
Today we removed the cartridges and rinsed them- they were visibly dirty and looked visibly cleaner when we were done. When we turned the filter back on after cleaning them it was great! Pressure stayed low on the gauge for hours! The output water was nice and strong for hours! (both were previously shooting up immediately after backwashing) Then when we looked about 8 hours later the pressure was up on the gauge and the output was low, so we backwashed. Pressure went back down and all looked good- for about 10 minutes then shot right back up.
I have no idea what's wrong here! I'm sorry for my lack of knowledge on filters and the vocabulary, any help you can give would be greatly appreciated- and I thank you in advance for your patience!