Pump flow rate dropping

Mar 24, 2017
I have a strange issue that I'm having a hard time troubleshooting and its driving me crazy. I have a 21' round 52" above ground Coleman branded pool (basically the same as the intex brand.)
This is the pump and sand filter I'm using:
Amazon.com : Intex Krystal Clear Sand Filter Pump for Above Ground Pools, 3000 GPH Pump Flow Rate, 110-120V with GFCI : Swimming Pool Sand Filters : Patio, Lawn Garden

The 3000GPH version.

Everything will work great when I first turn it on, but over time the flow rate drops. In less than an hour the flow rate goes a trickle. I check the pressure gauge on the sand filter and its in the green. If I turn the pump off, switch to backwash, then the pump performs the full backwash and rinse perfectly. I can flip it back to filter, and I'll get that good flow rate again, and then after a time I'll get the same issue where the flow rate drops off.

Could there be something wrong with the sand filter that's causing this?

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Hello and welcome to TFP! :wave: I would doubt the sand is at fault unless any unusual pool store products were added previously that may have compromised it. I would be very curious to see your chemistry test results first. Do you have a TF-100 or Taylor K-2006C test kit? That would be important to know first before assuming there is any hardware issues. Can you post:

Great to have you with us at TFP!
Mar 24, 2017
There's a hardware store that does the full testing for me for free. I Just refilled the pool for this season, so its pretty much just city water.

Free Chlorine: 0
Total Chlorine .3
CYA: 0
PH: 7.8
Total Alkalinity: 126
TDS: 200
Hardness: 213
Salt: 100

I just added salt and conditioner to the pool after this test.

This is my 3rd year with the pool, I got the pump/filter last year and have had the issue since day 1. Intex didn't really have any answers for me.


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

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

Sounds to me like your filter is doing exactly what a good filter should do, and that is taking all the dead stuff out of your pool water... :cool:

Really, the number one reason for the filter to act like yours is the something is in the water that quickly fills it up. This is also why it works after you back wash it.

With a CYA level of 0, any chlorine you put in your pool will be gone in an hour or so.

I assume you have a Saltwater Chlorine Generator (SWCG), if so, your CYA level should be about 70 ppm... And your FC should be around 5 ppm. See this chart... https://www.troublefreepool.com/content/128-chlorine-cya-chart-slam-shock

This web site is dedicated to showing pool owners how to care for their pool, but testing their own water and knowing exactly what needs to be done to keep their water crystal clear..

You can read more by using the Pool School link at the top of this page.

Thanks for posting,

Jim R.
Mar 24, 2017
See, that's the odd thing. There's really not much in the water its clean straight from the city, and the sand system still reads green pressure when the flow rate drops. I thought that you really should only need to backwash the filter once a week or so for normal operation. I have to baby sit the filter and backwash it at least once an hour just to keep the flow rate up, that doesn't seem right.

I've added Salt, Cyanuric acid (conditioner), and shock to the pool after the test was taken. I wanted to be sure the PH was in the right levels before I added anything.
Mar 24, 2017
Ok, I just did another test. I waited for the flow rate to get really low, then I did the following:

turn the pump off
switch to "recirculate"
turn pump on.

flow rate was crazy high, better than I've ever seen it. Then I did this:

turned the pump off
switch the filter mode back to "filter"
turn the pump on.

flow rate is back to being good again. So, I'm not sure what's going on, but backwashing isn't even necassary to get back to full flow rate.

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
It's always possible the gauge itself is going bad. When you turn the pump off, does the needle fall all the way to zero? You might also check the return jets to see if the return flow (pressure) feels the same throughout the day - nice & strong.

As for the chemistry, we always remind forum members that while convenient, local pool store testing is usually unreliable. Causes for this include improper (incandescent) lighting, poorly trained/seasonal employees, and/or industry-generated recommended chemical recommendations that are outdated. Simply put, you'll get the best value and accuracy by testing with your own TF-100 or Taylor K-2006. As Jim noted, if we were to assume those local store test results were correct, your sanitation levels need some immediate attention. FC should never be that low, in most cases never below 3 or so, and often times should be higher based on the CYA. Since your CYA seems to be non-existent, your FC has no protection, and any bleach/chlorine added it potentially much stronger in the water without the CYA (stabilizer) to serve as a buffer.

You really would be best served to test your own water and use the TFP recommended chemicals/levels to adjust accordingly. If you have any further questions, please let us know. Have a nice weekend.
Mar 24, 2017
Gauge is fine, it goes to 0 when turned off. Not sure what you mean by return valves, I have an AGP. The low flow of water going into the pump and out the return is why this is an issue.

Did another test, flow rate was dropping after lunch, so I turned it off and just pushed the handle in on the filter without changing it off of filter mode. Turned it back on and the flow rate is back up.

There's definitely something going on with the filter. I'm going to have to take it apart and see if I can figure it out, just maybe not in the middle of the day with the sun directly overhead.


Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
Sebring, Florida
See, that's the odd thing. There's really not much in the water its clean straight from the city, and the sand system still reads green pressure when the flow rate drops.
You can't see the stuff that is clogging your filter. As JimRahbe says your filter is clogging up. Gauge in the green is irrelevant.........that gauge is not good enough to help you.

How do you fix it?

You have to SLAM the pool and you have to understand it is invisible stuff that is clogging your pool but it is about to get MUCH worse unless you get some chlorine in your pool. There is a lot of learning to do but I want to assure you of two things...

1. It is live organics (invisible alga) that is clogging your pool filter.

2. We will help you every step of the way if you choose to take the path of learning that TFP promotes.

Pool Clown

In The Industry
Sep 5, 2008
Silicon Valley, CA
If you have had this issue for a year, i offer that it may not be a chemical issue. I think it would be difficult to be inadvertently keeping the pool on the verge of turning green for that long. You didnt report that the pool was green.

I could be wrong though...

If it isn't chemicals, it could be something with your filter media. What type of sand did you use? Was it #20 silica sand? or was it, and forgive the possible insult, any or the cheapest "play sand" you found at the hardware store? There is a right and a wrong type of sand to use. The correct sand is usually a bit more expensive than other types.

The low pressure is interesting, i too would suspect the pressure gauge. A new gauge shouldn't break the bank, i would try that first.

Another thing i might check would be the suction line from the pool to the pump. If flexible line was used, it is possible it may be collapsing. Also check the line for obstructions, strainer baskets that are full, etc. Your pump probably has a threaded plug somewhere in the low pressure (suction) side where you could purchase and install a vacuum gauge. The reading on that gauge would tell if you are having problems with the suction line having an obstruction or collapsing. Anything higher than 10-15 Hg of VAC would indicate a problem with the pump getting water.
Mar 24, 2017
Pool's not green, I had to empty the pool last year and just filled it up with city water yesterday. Got the water tested first and then just added the chemicals and salt, so I just need to re-test to verify everything is good.

The pump/filter has been doing this out of the box since I got it. Beginning of 2016 I had a dead stock filter pump and a DARK green pool. So, I upgraded from the standard filter-pump to the sand and pump combo I linked earlier. Had to backwash constantly because of all the junk in the pool, but I got it crystal clear. It wasn't until everything got settled in and the water was clear that I was still having to backwash constantly or lose out on flow rate. I called intex about it late in 2016 and didn't really get anywhere with the guy on the phone. So, I just dealt with it, constantly backwashing to keep the thing flowing.

Now, at least I know that all I have to do is turn it off and depress the handle and then turn it back on and I get the flow rate back. This makes me think that maybe somehow air is getting trapped in the top of the sand tank, if that's even possible. Maybe there's a small crack somewhere in the top of it.

As for sand, I'm using Quikrete brand Pool Filter Sand.

I am using flexible line to connect everything. I couldn't find any blockages, and I don't think its collapsing but I can double check.


Well-known member
Jul 15, 2013
I had a similar thing happen to me with my old DE bump filter. Nice flow for a while, then it would cut to virtually nothing. Nothing on the pressure gauge either. I'd turn the pump off, bump the filter, turn back on, and get great flow for a couple hours. Then nothing again.

I got rid of the filter and the problem went away. Maybe you need new sand. I don't know about sand filter maintenance.
Mar 24, 2017
Think I got it fixed. I took the sand filter completely apart and cleaned everything out. There was actually some gunk in the top part of the system, where the handle is. I did a "deep clean" of the sand media, which was mentioned elsewhere on this site. Put everything back together and started it running.

Its been an hour and its still going strong.