Filter is more sensitive after pump upgrade, needs more backwashing

[pcm2a]

My previous pump was a 15 year old Northstar 1.5hp single speed. We upgraded it a couple months ago to a 1.85 HP TriStar VS 900. The new pump runs great but it is requiring more backwashing. What I notice after about two weeks is at a slower speed 2250 my spillover should be running pretty good, instead it will barely be running. Similarly at a fast speed 3100 the spillover is just going at a medium rate. I backwash the filter and poof everything is back to normal.

On the previous pump (single speed) the flow of the water was always the same. I would watch for the pressure to rise to know when to backwash. I would backwash every month or so. On the new pump at the time of backwashing the pressure is identical to after the backwashing (much lower than the old pump). Example, running at 3100rpm visually looks about the same at the spillover and at the jets in the pool as my old pump. The pressure runs about 15 where on the old pump it ran around 20. I don't know if that pressure makes any difference.

My question is, why does the new pump require more backwashing?

Before backwashing:

After backwashing:

 

[RDspaguy]

Your old pump ran at 3450rpm, just for reference.
It is a sand filter, I assume? Sounds like you need a deep clean or new sand. As sand filters out the water it accumulates oily residue on the surface of the grains. This residue causes it to stick together in clumps, reducing your effective filter area and causing it to clog up faster. I believe TFP has a link for the process, but I am not sure how to find it.
Maybe one of the long time users knows? Lets see if I can do this...
@kimkats, @mknauss, you seem familiar with all the links. Can you lend a hand?

 

[mknauss]

Sand Filter Use and Care - Further Reading

www.troublefreepool.com

Deep Cleaning a Sand Filter

This post will walk you through the anatomy of a sand filter, and then provide a video at the end for how to deep clean your sand filter. The filter used in the photos and videos is a Hayward S180T top mount sand filter. The images are of a similar filter. Obviously not all filters are...

www.troublefreepool.com

 

[pcm2a]

The key thing is this only started with the new pump. Maybe the sand is old and needs to be replaced but why did the new pump with old sand make the issue start occurring? My only guess is something to do with the pressure, because it was higher pressure on the old pump.

Your old pump ran at 3450rpm, just for reference.

Absolutely. When I run the VS pump at 3100 it visually looks the same at the spillover and at the jets as the single speed 3450 pump. When I run the VS pump at 3450 there is lots more water coming down the spillover and at the jets than the old pump could ever deliver.

 

[Jimrahbe]

2a,

Let's forget about your new pump for a minute and just think about the filter... When someone says that they have weak flow, that is temporarily cured by back washing, it is almost always because of an Algae bloom. Even if they can't see it.

My recommend is to do an Overnight Chlorine Loss Test (OCLT) , just to make sure. Overnight Chlorine Loss Test

I suspect that the new pump has just made the problem appear worse..

I think having to backwash one a month is excessive.. I have two rent house pools with DE filters that never get backwashed,.. I just clean them twice a year.

Thanks,

Jim R.

 

[duraleigh]

+1 what Jimrahbe said. Clogging the filter is a function of incorrect chemistry and is not related to your pump.

Can you post a complete set of test results?

 

[pcm2a]

I don't know if I should have been backwashing once a month or not. I read to watch the pressure and when it goes up to backwash. I'd check it monthly and if it was higher than 20 I'd backwash. Sometimes it was longer than a month, and never in the winter once all the leaves were gone.

I stay on top of the chemicals so I'll remain skeptical that it's the cause... Below are readings taken just now.
Pool temp: 66, Air temp: 64
FC: 3.4, pH: 7.8, TA: 80, CH: 240, CYA: 50-60 (tested 2 weeks ago)

I'll do the OCLT test tonight to confirm.

Another idea is could it have anything to do with the times/speeds I'm running the new pump vs the old pump?
Old pump: 14 hours on, 11 hours off (not continuous 14 hours)
New pump: 24 hours on, varying speeds from 1150 to 3100 throughout the day

Update: Thanks for the link to the deep cleaning. I have never done that in the 3 years I've lived here and I seriously doubt the previous owners ever did. I'm not sure how I would get the lid off without cutting some pipes but I can create a separate thread if I decide to tackle that.

 

[duraleigh]

I stay on top of the chemicals so I'll remain skeptical that it's the cause

Something is clogging your filter.....let us know when you find what it is.

 

[RDspaguy]

Cut it out and reattach it using unions so you can get into it next time with ease.

 

[Jimrahbe]

Not to be picky, but with a CYA of 50 your FC should be about 7 ppm..

Jim R.

 

[pcm2a]

Would it be beneficial to get a bottle of the sand filter cleaner before going for the deep clean?

I'm going to have to cut 3 pipes and add 3 unions in order to get the lid off (or pay someone due to my poor skillset). The pipe work also leads me to believe that it has probably never been deep cleaned. Could the lid be disconnected and the filter slid out, I assume it's heavy.

 

[pcm2a]

Not to be picky, but with a CYA of 50 your FC should be about 7 ppm..

Yeah it will get some chlorine added in tonight before I do the OCLT.

 

[RDspaguy]

Not to be picky, but with a CYA of 50 your FC should be about 7 ppm..

Jim R.

Jim, I don't know you well yet but I get the impression that "picky" is as much a part of your genetic makeup as it is mine.

Pcm, heavy does not begin to describe it. You have plenty of open straight pipe to work with, simply cut at least 2" from any other fitting and glue in a union, which is a threaded compression fitting you can unscrew and disassemble. Nothing to it. I am sure you can manage for less than $50.

 

[pcm2a]

I've worked with the piping before to install a check valve so maybe I can accomplish it. Hardware store sells the 2" pvc unions for $14 each plus the 2 pack of Oatey. I guess that's a better investment than the pour in cleaner. I should pick up a replacement o-ring for the lid before doing anything?

 

[RDspaguy]

If it has never been serviced, which seems likely, I would replace the o-ring just to be safe. Unless you enjoy taking your filter apart, that is. It will be much easier with unions...

 

[pcm2a]

FC test 11pm last night 5.2.
Today at 9:15 am it is 4.6.
I got the unions yesterday and I am going to start with the backwash pipe since that wouldn't affect the pool if I botched it.

 

[Flying Tivo]

You got it! If it where me, i would also go in and check the spider gasket in the MPV. If in good condition just lube it up, if not you can change it.

 

[pcm2a]

It's time for a quick update here. I have removed all of the sand from the filter. I have replaced the lateral with a brand new one and the sand with 300lbs of pool filter sand (home depot). I also replaced the multiport with a brand new one. I backwashed and rinsed twice. It has been running for a couple hours and at 2250 rpms the pressure is at 9. Before I changed all of this the pressure was at 7. The water flow at the spillover is slightly less than it was before. The big question will be, does the flow reduce after a couple weeks like it was before.

Here is a video of my spillover at 2250 rpm, it has a little less flow than before. You can compare it to the videos in the original post:

 

[Flying Tivo]

How are your valves set? Post picture please.

 

[RDspaguy]

When sand is clumping the pressure of the pump can blow holes through it, forming a "sand pipe", if you will, that allows water to pass throught the filter with little resistance. We call this "channeling". New sand, working as it should, could very well impede water flow more than the old sand did because it is filtering the water better.