Backwashing questions

I have an IG 20,000 gallon pool, using a sand filter. Last year I didn't have to backwash very often once my pool was up and running. I did it maybe once every three weeks or so when I noticed a lot less water flow through the system or a much higher water pressure on the gauge. This year, I'm having to backwash about once a week. It's really not a problem to do so, but I'm wondering about the change.

Also, I remember reading once that when you backwash you should do so for three minutes and then rinse for 30 seconds. Is it necessary to backwash for three full minutes even if the water in the little viewer bubble looks clear after only one minute? I don't want to send my pool water down the drain for two extra minutes if I don't have to.

What do backwashing and rinsing do, exactly? How do I know when to add or change filter sand? I changed it two years ago, BTW. Does it need "topped-off" every once in a while?

Backwashing reverses the direction of water flow through the sand to wash out the debris the filter has caught. Rinsing runs the water through the filter in the normal direction, but the output goes to waste instead of the pool. This prevents any debris that got caught during the backwash or came loose during the backwash from entering the pool.

Don't worry about your sand. No maintenance required unless you have filter problems.

OVER backwashing can actually reduce the effectiveness of a sand filter. That includes doing it too often or for too long. Some amount of debris in there helps filter more.

We backwash only when we start to have pressure issues and then only just until it looks clear. You should not have to change/empty your sand unless you have a big problem with something like laterals, but frequent backwashing may wash some amount of sand out after time so you may need to top off if you have been doing it a lot.

I backwash until it's clear and then rinse til clear. Both usually start out clear - then dirty - then clear again.

I inherited my pool 7 years ago and just changed the sand over the weekend for the second time this past weekend becasue I was backwashing all the time. Took a couple hours and $25 for 150 lbs. of sand. I add a little DE to my sand through the skimmer which greatly enhances filtering but does cause me to have to backwash a little more often. Well worth the price for crystal clear water!