"Phantom" Pressure Rise after Adding DE

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skillset

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May 3, 2007
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Central NJ
Last year I was able to add a cup of DE to my Hayward sand filter to get better filtering. This year, when I add the same amount of DE, the pressure goes up about 0.5psi every 45 minutes. The VERY strange thing is when I shut off the pump, but the filter on backwash (but not turning on the pump), then put it back to filter, and turn the pump back on, the pressure drops to about normal clean pressure. I will have to backwash the filter to remove the DE because I don't want to have a situation where the pressure is rising for "no good reason." I originally thought the pressure rise was due to the increased filtering, but I guess not, since pressure returned to just about normal without backwashing. I can repeat this cycle.

Any explanation on why this is happening in the filter ?
 
What does your water look like? Is it sparkling clear, clear but dull, or cloudy?

Most likely your pool has a lot of fine debris that is only getting caught when you add DE. Once the fine debris is all caught and removed the rate of pressure increase will drop back to normal levels.

If the sequence is just as you describe it, with the multi-port valve having to be put in backwash position to stop the pressure increase, the most likely cause is a syphon causing the filter to backwash enough to remove the DE even with the pump is off.
 
Thanks - I have another post you replied to on cloudy water with cal-hypo I added, so my water is currently cloudy. This is a situation I rarely have and am not used to, at all! Interesting answer on the syphon. In the last 90 minutes it rose 0.5 psi, but again, just putting the filter on backwash (pump off) for a few seconds and then back to filter gets the pressure back down. Anyway, I didn't want to take the chance or running it overnight and risk the pressure getting too high so I did backwash all the DE out. So, pressure back to normal 20. Perhaps I'll try using 1/2 cup of DE. I was hoping to accelerate getting the water fixed!
 
You will fix your pool water with balanced chemistry. Please post a set of test results so we can get a better picture. If you are running another thread simultaneously, it is very confusing to those of us trying to help many people.

Please keep all your posts under this thread from this point so we can see your whole story.

Your filter issue makes perfect sense....it is doing it's job of filtering out fine particles.
 
With cloudy water, the added DE is catching the particles causing the water to cloud up very efficiently, thus the pressure is going up rapidly. That is exactly what you want it to do. You should let the pressure go up to your backwash pressure, backwash right away, add more DE and repeat. That will clear the cloudiness fairly quickly.

By the by, it is generally better to keep everything relating to a single question or project together in one forum topic for this exact reason.
 
Ok - I'll keep this thread solely to the DE / Filter question. My other thread is much more involved regarding cloudy water. Anyway, I recently changed my sand and again am trying to use DE to improve filtration. Same thing is happening where I'm getting a "phantom" rise, but I found an easier way to relieve the pressure. With the pump off, simply pressing up on the multi-port valve for a few seconds relieves some pressure. For example, started yesterday with a new gauge and clean pressure of 20 at 9PM. This was right after the sand change. Next day at 5:30PM, pressure was 21. So, up 1 lbs. Added enough DE at 5:30PM to get just shy of 22. After 2.5 hours, gauge read 24.5. So, was the DE working over that 2.5 hour period? Relieved the pressure as I described above which got it back down to 22, which was a slight rise from when I added the DE, but by no means a full 2.5 lbs!

Thus I'd like to ask 2 questions given the possible siphon point above:

1) If the pressure is going up, but is able to return down just be relieving some pressure, I'm assuming I wouldn't backwash until I'm REALLY experiencing a high pressure rise due to trapped dirt, correct?
2) Given that I just got new sand (and a new lateral assembly), I'm assuming the filter is working ok with what I describe?

Happy 4th!
 
As I said last time, you should let the pressure go up to your backwash pressure, backwash right away, add more DE and repeat. You should not be playing games to get the filter to read a lower pressure, which will just make the entire process take longer. As long as your water is cloudy this is normal and to be expected. If it bothers you, stop adding DE to the filter.
 
Ok, thanks for the reply, especially during the holiday.

It's not bothering me, I just don't understand why the pressure can come down without a justification. But, I'll follow the advice as the pool is definitely still cloudy.

Thanks again.
 
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