Surging sand filter pressures

[C3Cl3N3O3]

So I have metals in my pool and am currently doing a weekly maintenance dose of Jack Magic Vinyl Blue. I did a citric acid treatment approx 1 month ago and my daily chlorine usage has returned to normal (2 ppm/day). Here are my numbers:

FC: 7
CYA: 50
TA: 70
pH: 7.4

I started adding DE to my sand filter a few weeks ago. Here's my issue. After a backwash, my sand filter runs at 16 PSI. I determined that 1 lb of DE will raise the filter 1 PSI (considerably more than the 4 cups or so recommended on the TFP). So my filter will then run at 17 PSI for a while, usually several days. Then, the pressure will suddenly spike 1 - 3 PSI very quickly. Today, after vacuuming and backwashing, I added the DE but dropped it down to 1/2 lb and added the maintenance dose of sequestrant. The PSI only raised up to 16.25 or so, not quite 16.5. It stayed there for a few hours, then suddenly jumped up to 20. The water is crystal clear.

So if I am filtering out metals I can stay the course. However, I feel like I may just be wasting water and DE. Any suggestions? I can't be backwashing twice in one day.

 

[duraleigh]

You are not filtering any metals. If that's your reason for the DE, there is no point.

What does your water look like? Do you think it will look good without the DE?

 

[C3Cl3N3O3]

It has improved the water clarity a bit, although it was pretty clear before. If it is going to cause me issues I can discontinue it. I'm just not sure what it picked up to jump 3 PSI in a couple hours with crystal clear water. I do have some possible indications of metals precipitating out, however it is hard to differentiate between that and normal debris on the liner.

 

[C3Cl3N3O3]

So I've got a theory. I get a fair amount of debris on the bottom of the pool at times, especially after any rain. If I run a manual vacuum instead of the robot, I think much of the debris that doesn't get vacuumed just comes off the liner and floats around. Then it heads for the sand filter. So the lesson here is not to backwash immediately after vacuuming. I should wait an hour or two. Or, just run the robot (it has a 4 hour cycle and an internal filter bag).