Water not Flowing due to Cartridge Filter

[DamnPants123]

Hello everyone,
This is my first time posting a thread here in Trouble Free Pool, I look forward to working with you all on this issue
I have a Pentair FNF Plus with 48 sqft cartridge filter and Pentair IntelliFlo pump
Recently, the water flow has become weaker more frequently around 1-3 weeks after cleaning filter and tank instead of 4-6 months like before
I decided to diagnose and found out the cartridge filters are the main problem after taking out the cartridge filter to see if the water flows faster, and it did
I have attempted to backwash the filter, but the handle seems to be stuck and I cannot switch to backwash
My pool filtration system looks like this one in the Youtube video: Cleaning a Pentair FNS Plus Filter & Troubleshooting
Should I replace the cartridge filter or there is a different problem?

 

[reggiehammond]

The “stuck” handle is concerning, but you report that flow is normal with filters removed.
Any pool store potions or other items added to pool water that could have blocked up filters?

Ever run the filters without DE?

 

[sande005]

Sounds like the filter is doing its job. Flow will get weaker as it gets dirty. What pressure do you have after being freshly cleaned, and at what is the pressure after the 1-3 weeks? A housing with no filters has nothing slowing the water flow, so of course it will seem to be great.
You just can't do maintenance like you should on it. Fix/Replace that backwash valve so you can actually backwash it.

If you've taken it apart and really cleaned it, then look to your pool. Post your test results from a valid test kit (not pool store or strips). Is the water crystal clear, with no trace of algae (alive or dead) anywhere?

 

[pjt]

I have a Pentair FNF Plus with 48 sqft cartridge filter

You have a DE filter, not a cartridge filter.

Recently, the water flow has become weaker more frequently around 1-3 weeks after cleaning filter and tank instead of 4-6 months like before

That often suggests algae.

How are you testing?

 

[Newdude]

That often suggests algae.

+1

99% of the time fast filter cycles are chemical problems not mechanical problems.

 

[DamnPants123]

Thank you very much for your responses

The “stuck” handle is concerning, but you report that flow is normal with filters removed.
Any pool store potions or other items added to pool water that could have blocked up filters?

Ever run the filters without DE?

I don't think I have added anything that could block up the filter, considering I have only used products from Leslie and Home Depot
I don't remember all the products that I use, but I still have some of them

Spoiler

Leslie:
- Algae Control
- Filter cleaner
- No Phos
- Power Powder Plus
- DE filter

Home Depot:
- DE filter
- Clorox Pool and Spa Shock XtraBlue
- Pooltime Algicide+ Clarifier
- Pooltime Jumpo Tab

I used the products as according to the instructions on the label. No, I don't use products from two retailers altogether on the same day.
I did run without the DE filter, it takes about 2 days slow the flow.

Sounds like the filter is doing its job. Flow will get weaker as it gets dirty. What pressure do you have after being freshly cleaned, and at what is the pressure after the 1-3 weeks? A housing with no filters has nothing slowing the water flow, so of course it will seem to be great.
You just can't do maintenance like you should on it. Fix/Replace that backwash valve so you can actually backwash it.

If you've taken it apart and really cleaned it, then look to your pool. Post your test results from a valid test kit (not pool store or strips). Is the water crystal clear, with no trace of algae (alive or dead) anywhere?

I cannot tell the pressure as the pressure gauge is broken and I have yet to find a place to buy individual part.
I have attempted to fix the backwash valve but it seems the inside of the handle is made of metal and had become rusty
With the backwash valve stuck, I have no choice but to manually open the tank and clean the grid and replace the DE filter

You have a DE filter, not a cartridge filter.


That often suggests algae.

How are you testing?

Sorry, grid not cartridge, I did not know we call the other one grid.

Few tests I have:
- Run without DE - 1-2 days to slow the flow
- Run without the 48 sqft grid and DE - water flows smoothly but no algae is cleaned

+1

99% of the time fast filter cycles are chemical problems not mechanical problems.

That is true, I observe no malfunction on the pump as it can pump water strongly after fresh cleaning.