Those of us that have to close their pools for the winter have no choice but to break everything down and clean once a year. I have one of those Hayward DE filters with the "fingers" - when pressures rise you just bump the handle a couple of times and you're done.

However, the whole idea of HOW this works totally baffles me. (The filter starts getting dirty and the pressure rises. You bump the DE off the fingers, start the pump and everything technically just attaches back to the fingers...dirt and all. Why does the pressure not just go right back to where it was? The dirt's still there!!!!)

It works because before you bump it, the dirt is sitting there in a fine, uniform layer that effectively restricts water flow. When you bump it you bust up that thin layer, so even though the dirt is still there, it isn't forming a barrier to water flow anymore.

That makes sense. Thanks. Another of life's mysteries solved.

I'd guess that, in a well-maintained pool, you could go many years without a problem. I am running a DE filter for a six-month season since 2004. I never backwash, except to close. I never soak in detergent or acid wash. I gently pressure wash the grids, using my weakest nozzle and maintaining a two-foot distance. The grids are pristine. I maintain strict water balance and I have never once had an algae bloom since switching to BBB from pucks in 2006. I also have a low use pool and any lotion users are told to shower off before swimming. The family all tans and does not use lotion, so this is not that hard to enforce on my adult user base.

What I can confirm is that even thorough backwashing always leaves some DE behind. Individual grids remain covered by as much as 30%. I'd estimate an average of 15% is still stuck when I break it down every year. Presumably, once 85% of the DE is gone, the water flow through the grid is so 'easy' that there is not enough reverse pressure to break loose the remaining 15%.

I would think that, if not removed by periodic cleaning such as I do, eventually these continents of DE would grow and create clogs in the system. Your filter efficiency would drop as time went on and intervals between backwashes would reduce. However, some portion of your filter would always be cleaned out. In a well-maintained pool, you might reach an equilibrium, where the diminished filter is still able to do a good job of cleaning at a slightly higher initial pressure, as long as serious stress is not placed on it, such as an algae bloom or dust storm.

I'm no expert, and I'm just speculating based on my experience and encouraging you to stick to your guns.

Beez,

I recently took my filter apart and cleaned it because I was getting DE in my pool. I was surprised how easy it was. First, the powder leak was caused by a hole in the air bleed valve. Anyway, my thought is that by taking everything apart, if not careful, I think you can easily break a grid and cause a problem that wasn't there before.

Otherwise, I question how often you should backwash, and if the number of backwash/recharge cycles is more important than the amount of time between full cleanouts. I only have to recharge about every 3-4 months, and usually that is more because I start to feel like something's gonna go wrong if I don't. Usually in that time, my pressure is only up about 3-4 PSI. Bottom line, I think if you had to recharge frequently (monthly), breaking it down yearly might be necessary because more and more residue gets left behind. But if you are only recharging 2-3 times per year, not sure it is necessary.

The final comment: If you wait a long time to take it apart, and when you do there is a lot of residual DE powder left behind, I believe the risk of damage is greater as everything gets very heavy and harder to work with (the pump shell itself is quite expensive, and I know of people who have had to replace one that cracked). My plan moving forward is to do an annual clean, but that simply will mean shutting off the pumps, drain the filter, take the top off, and rinse as much off through the filter drain. In other words, everything I can do without pulling the grid assembly out and apart. It's very easy to do, shouldn't take more than 10 minutes. Now the question I have...is it really necessary to backwash more regularly than I do?

Well, better you than me! But I guess this is how the science of pool care advances--through experimentation. Exactly how long are you planning to keep this up? As soon as you see signs of damage, are you going to reverse yourself and abide by cannon, or will you continue to experiment? The rest of us can be your control group

I plan on continuing as I have until I see a persistent pressure rise, or some other definitive problem. I will update this thread with the results when I eventually do break it down. I really don't think I'm risking that much, I can replace the complete grid assembly(including manifold, rods, etc.) for $300.

Of course, I could be wrong...

Update:

Had to open the filter because of DE leaking back to pool through the returns. Expected the worst, but all is well. The problem was a collapsed screen on the manifold. Grids look great. Minimal DE accumulation even though filter hasn't been opened in 4 years. A happy report!

Thanks TFP!!!