I have an above ground pool with the thick vinyl. It is 16' X 24' rectangular. 3.5 feet in the low end and 5 feet deep in the deep end. It is roughly 12000 gallons. It has a Hayward S-180T sand filter. Also I am on a well system.
After I back flush and rinse the filter it runs at about 14 PSI with really powerful return jet. After about 30 minutes the pressure goes up to about 20 or 21 PSI and the return jet is really weak. I have back flushed it about 4 times now and always the same result. It will run strong for 30 or 40 minutes then it goes weak again. When I put the system on recirculate it runs at a constant 12 PSI. I just replaced the gauge 2 days ago so I know it is working properly. I am not sure when the previous owner changed out the sand last. Any ideas of what could be causing the pressure to rise up so fast and the return pressure to drop so low? The water in the sight glass when back flushing doesn't look very dirty at all. I wouldn't think it could get that dirty that fast to cause this rise in pressure. Any help would be appreciated. Thanks.