shocking causing low psi

[jasonnn]

Hi all, I have what I (and a few others) suspect is mustard algae in my saltwater fiberglass pool. The mustard algae is on the pool floor and steps. I don't think this is dust. There's no similar dust on stuff near my pool. So I started slamming. My test numbers are all good, it sucks that I have to do this to a pool that has crystal clear water. Now that i've begun shocking, my sand filter psi is dropping really low, which never happens. The normal psi is 12. With shocking it's at 3. So, i backwashed and it went back to 12, only to go back down to 3 within 45 mins. I've done this backwashing three times already now whilst shocking. Anyone know why this is happening? There's no blockages (I even checked, and had to reprime). So confusing as to why it's happening.

Thanks.

 

[jasonnn]

forgot to add: i'm slamming with liquid chlorine.

 

[pabeader]

What psi does it read when the pump is off?

 

[jasonnn]

From memory I think it reads zero. When the psi goes low whilst shocking, the return jets are hardly doing anything.

 

[pabeader]

Sounds like your pressure gauge is working backwards. But, you are killing something in your pool so that's good. Just keep up the good work and watch the gauge as you have been. Usually the pressure goes up when the SLAM is working it's magic, for some reason your gauge is registering it in reverse. Must be plumbed on the output of the filter instead of the input.

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Just a note: We call it SLAMming, instead of shocking. SLAM stands for Shock Level And Maintain. Keep the chlorine up where it needs to be in relation to your CYA and test it often.

 

[pooldv]

That is very strange. Normally pressure goes up and water flow goes down as a filter gets clogged up. Also, normally lower pressure in the filter equals higher flow rate from the pool returns.

 

[pabeader]

Here is an article about it: Pool School - SLAM - Shock Level And Maintain