low flow from filter/high psi


New member
Aug 15, 2016
Hendersonville nc
we are at our wits end.We have a new 24' above ground pool.
It was installed last august and all was fine. We closed the pool and just opened it about 2 weeks ago.
We did all the recommended steps. The initial psi about 12-15. output flow was strong. Then the next morning
we noticed the flow was very weak and the psi 20.
We completely cleaned the pump and impellers. We removed the sand from the filter cleaned everything and replaced it with new #20 silica sand.
We back washed, rinsed and restarted the system. Psi again about 15. and STRONG flow from the output. After about 4 hours
again the psi were about 20 and the flow almost nothing. We have redone everything several times all with the same results.
We are frustrated and don't know what to do.


Mod Squad
TFP Expert
LifeTime Supporter
Apr 17, 2010
East Texas
Welcome to the forum. Gotta ask..................does the pool have green algae in it. Full of leaves or pollen? Is the water clear? No need to change the sand btw.
Got any GOOD test results for us?


Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
Bedford, TX

Welcome to TFP.. A Great resource for all your pool questions. :snorkle:

You might not know what to do, but your filter does... :cool:

Your filter is doing what it should by capturing all the dead junk in your pool.

There is almost never a reason to replace the sand, just backwash and rinse and repeat.

My guess is that your water is either green or very cloudy. This is an indication that you have algae and that is what is clogging your filter.

Assuming I am right about your water color, you will need to perform a SLAM... See this .... https://www.troublefreepool.com/content/125-slam-shock-level-and-maintain-shockingl

To perform the SLAM, you will need one of two test kits... either the TF-100 or the Taylor K2006C...

Here is another pretty good read.... https://www.troublefreepool.com/content/122-what-is-tfpc-bbb

Thanks for posting,


New member
Aug 15, 2016
Hendersonville nc
Sorry...no green algae water is clear
no leaves or pollen
one thing I forgot to post is that when we put the filter on recirculate the flow is strong.
not sure what you mean by good test results. We have done everything we can think of.
when the flow is weak if we turn the pump off and then on again everything works good. PSI 15 and strong output. then after a few hours psi 20 and almost nothing from the return line....

- - - Updated - - -

no green water. Its clear and all numbers are correct. I was a chemistry major in college....
We have the good test kit also....


TFP Expert
Apr 29, 2016
Quaker Hill, CT
When you recirculate you are bypassing the sand bed and not filtering the water. Like the others have said it sounds like your filter is doing its job and removing things from the water. If you do a backwash and rinse and the return goes back to normal then the filter is working and there is something in your water the filter is taking out. The water doesn't have to be green or cloudy for there to be an algae bloom in your pool that would clog the filter, but when we say clear we mean crystal clear to the point where you can see every little spec of sand on the bottom of the pool when looking at it from the deck.

By good test results we are looking for a run down of the pH, Free chlorine (FC), Combined Chloramines (CC an indicator of oxidized chlorine and presence of algae), Cyuranic acid (CYA), total alkalinity (TA) and calcium hardness (CH). If your test kits provides you will all these readings we would consider it a good test kit.

99 times out of 100 there is nothing wrong with your sand filter they are very simple things and don't fail often.

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