Listed below is the scenario:
I have 2 main drains, 2 skimmers, 8 returns. The pool was opened on April 26th, 2015. After the first few days, the pressure rose slightly and I backwashed just because it was the beginning of the season. Pressure usually runs around 13 psi. During the summer, I thought something was wrong with my gauge, and in order to rule out the "bouncing needle syndrome", I backwashed again. This was about 45 days later. There was no pressure change at all after backwashing. Sight glass cleared up real quickly (less than 1 minute), and water was not that dirty to begin with.
Since then, I have not backwashed the filter as the pressure has not increased more than 15% (at most). The pool stays relatively clean and I use skimmer socks to catch all the debris and swap them out weekly. When I vacuum, everything is caught in the skimmer basket (with the sock) and then replaced if needed. Have 3 sets of skimmer baskets with socks ready to go. Decided this during pollen season as the accumulation is quick and almost needs to be changed every few days, if not daily. I will backwash when closing the pool as water will need to be drained.
I know that the TFP rule is about 25% over normal starting pressure, while others tell you 10 psi over normal starting pressure. My "bouncing needle", (really not that much) all has to do with the plumbing and vibration. When I shut down the main drains, one skimmer, plus 4 returns, my pressure increases dramatically (over 20 psi) and the needle is fairly stable. The system was clearly oversized and pressure also changed after they added the 4 circulating heads. This kind of rules out the needle is defective. Needle always goes back to "zero".
In this situation, should I backwash at least every 30-60 days, even though pressure really does not change that much? Thank you.