Different amount of DE when back washing vs. Full clean?

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S

sijaz

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Jan 24, 2016
11
Houston/Texas
Hi, I am confused about one point. I have a 60 sq ft Pentair FNS 60 filter. Every 30 days or so when the pressure goes up, I backwash the filter and add 7 standard scoops of DE. Is this the same amount I would add when I do complete tear down of filter and wash out with a hose? Or do I need more (10 scoops) DE? THANKS

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The manual says 6 lbs for a fresh fill. That's how much you add after a full teardown and cleaning. After just a backwash, you should only add 80% since it doesn't all wash out.

You might want to doublecheck exactly how much your scoop holds. The reviews of the Leslies scoop indicates it only holds 12 ounces. If that's what you've been using, you've been overcharging your filter after each backwash. Might be time for a full teardown. Hopefully it won't look like the picture here: DE Filter Cleaning Tutorial
 
When tearing down and completely cleaning a DE filter, you use the recommended amount of DE to charge it up. For the FNS60 that's 6-lbs of DE. For a proper plastic DE scoop (they are usually bright orange colored), that's about 1-lb per scoop or six scoops. When backwashing the filter, you should only use 50%-80% of the recommended amount as backwashing does NOT remove all of the DE. Typically, if you tear it down and notice a lot of spent DE in the bottom of the filter, then you add less DE (50%) rather than more (80%) with backwashing.

It sounds to me like you are over-charging your DE with 7 scoops for each backwash you do. Of course, that depends on your scoop and how much DE by weight it holds.
 
The filter holds 6lbs. of DE when full. After backwashing you should be adding around 2/3rds of that amount which is 4lbs.

When I backwash my filter which is the same size as yours, I add 6 scoops of DE using the Leslie's blue cup. I have weighed the amount of DE that the Leslie's cup holds and it averages 3/4 of a pound.

The alarming thing to me is that you are needing to backwash every month. Are you in an extremely dirty area or something like that? If not, I have a feeling that you have a low grade algae problem that you have not detected and the dead algae is causing the rise in pressure.
 
Thanks for the replies. I will do a complete tear down this weekend and start over. Maybe my backwash frequency is the result of too much DE. Or perhaps the algae problem you're referring too. I just started on the BBB bandwagon and taken control of my pool, thanks to this site and a proper testing kit.

What frequency of back washing is considered typical/normal for properly balanced pool (e.g. for large 39k gallon, pebble tec in Houston)?

When I do a tear down, I take out the filters one at a time, clean, and replace. How do I get to the DE at the bottom of the filter....its just a pool of dirty water? The backwash is piped and I don't think there is another drain outlet on the filter unless I'm just not seeing it. Can I start the pump briefly in backwash mode (multi valve) with the top part of the filter off to help drain what's left in the bottom? Is that safe?

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There should be a drain plug on the bottom of the filter that is accessible from the outside. It's typically black plastic and it has an o-ring on it. It should be just below the threaded pipe connections.

See the owners manual - http://www.pentairpool.com/pdfs/FNSPlusOM.pdf


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006
 
That seems like a small filter (in terms of filtration area) for a pool your size. I have a 16k gallon pool with a QuadDE 100 filter (definitely oversized) and I only have to backwash 3-4 times per year with a full tear down once per year.


Sent from my iPhone using Tapatalk,16k gal SWG pool (All Pentair), QuadDE100 Filter, Taylor K-2006
 
I have the same size of filter as the OP but my pool is half the size, and my filter has gone a full year without needing backwashing.

To rule out algae as the culprit, the OP should run an OCLT, Overnight FC Loss Test. I suggest raising the FC level to around 10ppm for this test.

If the pool passes the OCLT then you might have to live with backwashing the pool monthly or getting a larger filter.
 
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