If you only backwash a DE filter (but not take apart the tank to clean everything) - how much DE to add?

anthonypool89

Gold Supporter
Aug 26, 2016
589
Berks County, PA
I read somewhere that suggested about 80% of the usual recommended amount. Another source said to use about half. I noticed that if I backwash several (shorter) times in succession - on/off with the pump for maybe 10 seconds each - then returning to regular operating flow in between to see what the gauge reads - the pressure is less after doing the successive shorter backwashes rather than if I do one long one (typically for about a minute). I usually always take the tank apart every time, but with the insanely short filter cycles I'm having, I want to experiment at least for a brief period with not always taking apart the tank - gets old after doing it every 3-4 days (actually now down to a single 24-hour period).
 

HermanTX

Gold Supporter
May 20, 2020
999
Katy TX
Pool Size
14600
Surface
Plaster
Chlorine
Liquid Chlorine
I do my backwash of a DE filter in short cycles (1-2 mins backwash, then <1min rinse) then repeat 3 -4 times. I look at my sight glass to see how much debris is exiting during each cycle. after backwashing I add 5 scoops (mine is a 60sq ft) of DE. The pressure drop between pre-backwash and post backwash (even after adding the new DE) is 8-10psi. When I do a complete clean - removing the filter grids and washing them down - I may add a 6th scoop of DE.
 

anthonypool89

Gold Supporter
Aug 26, 2016
589
Berks County, PA
I have 52 sq feet, and so put in 5 scoops. From what you're saying, seems about right. However, it didn't go well. I had shut the system down before going in for dinner (gauge was at 14 - not bad considering initial start-up after taking the filter tank apart is usually 13.5). Then, however, when I came back out to the pool and started up - it was 15. So did one more mini-backwash - added the DE - now at 16. I can't win. At most I gained a few hours. Betcha it'll be back up to 22 by 9:00 tonight. Time to dump the water, even though it's absolutely clear.
 

anthonypool89

Gold Supporter
Aug 26, 2016
589
Berks County, PA
You’ve got something else clogging the plumbing
Well, gotta say, that has been a suspicion of mine all along, which is what precipitated the use of the Baquacil Line Cleaner; however, I have as good a pressure from the return lines after backwashing and using clean grids, etc. as I ever have. I even did an experiment by running the pool for a time without the filter grids, and the pressure is about the same as it always was - and doesn't change. If there was a suction side blockage, I'd have lower pressure than usual. Vice-versa for pressure side blockage. I've been through this with many different people, and the general consensus seems to be against there being anything in the lines. I've been told it's all likely due to either organics or simply the biguanide. What's so weird is that THIS level of filter pressure increase is completely unprecedented. Nothing even close to it in the 31 years I've had a pool. Thanks for the suggestion though. I WISH there was some sort of blockage and that's all the problem would consist of. That'd be easy. Believe me, it has been driving me crazy trying to wrack my brain over just what could have caused this drastic a change in filter pressure increase.
 
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anthonypool89

Gold Supporter
Aug 26, 2016
589
Berks County, PA
You have a point. It'll be interesting to see what the filter situation is once converting to chlorine. If it's a similar pattern, then that leads me elsewhere. I'd just like an answer to everything that's going on this summer. I'm not one to give up easily (understatement, right???) 😆 Ah yes, my uncle was fond of saying, "life is good, if you don't get weak..." I will try to stay strong and forge ahead with whatever path this pool problem leads me on. There are worse things - like planning on going back to a teaching year under this covid environment (glad I don't have to). Speaking of blockages though, unless there is determined to be an actual break in the lines or similar - can't the lines simply be snaked like most plumbing issues? I have no idea since I've never had anything done with the underground lines.
 
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trivetman

Bronze Supporter
Jul 14, 2017
306
Jenkintown, PA
If you have the same pressure in the filter running with or without grids in, it sounds to me like you have something clogged between the filter and the pool. I would expect the pressure to be much lower. The pressure I think is created by the grids restricting water flow. Without them in, water should flow more easily hence lower pressure.
 

anthonypool89

Gold Supporter
Aug 26, 2016
589
Berks County, PA
If you have the same pressure in the filter running with or without grids in, it sounds to me like you have something clogged between the filter and the pool. I would expect the pressure to be much lower.
Sorry I didn't explain it clearly enough. The pressure IS lower without the grids in. When I said the pressure is "what it usually is", I was implying what it usually is without the grids - which is around 12-13. That's what it was when I tried it. The pressure is higher, however, when adding the grids - even without any DE - but it should be. If there was something clogged between the filter and pool, why is there such good pressure upon start-up once new DE is added? I don't think there is any blockage. If there was, it would produce higher pressure immediately rather than a normal start-up psi and then a gradual (though fairly rapid) increase. I appreciate your input, but highly doubt that this is a blockage issue.