Unreliable PSI changes when adding DE to a sand filter

[tjhm4]

Following advice in this thread I have added some DE to my sand filter to improve filtration. However, the resulting PSI changes are inconsistent so I'm wondering if something is off. Here's the data:

Round 1

1. Filter was initially at 12.25 PSI
2. Added 1/4 cup of DE at a time until filter reached 13.25 PSI. This was a total of 3/4 cup of DE.
3. I set a limit of 15.25 PSI before I would backwash the filter and repeat
4. Filter increased to 15 PSI in the next 2 hours, at which point it just stabilized
5. 1 hour later I decided to backwash, discharge was very cloudy for ~3 minutes

Round 2

1. Filter was now at 12 PSI
2. I added 3/4 cup DE but PSI did not change at all
3. Pump has now been running for ~45 mins and PSI has increased to about 12.5

So I guess the main oddity is why the PSI didn't increase when DE was added in round 2. Aside from that, 3/4 cup of DE is lower that what the TFP article expects.

Any insight would be greatly appreciated. Thanks!

 

[YippeeSkippy]

Perhaps like flour- if packed in it will weigh more but if loosely scooped up you have less of it.

Maddie

 

[tjhm4]

Thanks Maddie. This morning I backwashed again and this time I added 2 cups of DE. Still no initial PSI change, but PSI does slowly climb over the next few hours. It's definitely working (pool getting clearer, backwash water filthy) but I guess there's something odd about my filter/pressure gauge...