Poor flow with FNS 60

[ayouard]

Hi
I have a problem with flow through my Pentair SVRS and FNS 60 filter setup. Everything has been OK until a few days ago when we noticed that the flow light on the SWG was red. Flow through skimmers was minimal and output from returns was weak. In addition the pump stopped and restarted several times as if something was blocked

With the multiport set to Recirculate everything is good, so we concluded the filter was the problem, even though psi had only risen 3 or 4 since I did a complete tear-down a month ago.

Backwashed yesterday, PSI was back to normal and flow was good. I only added 4lbs of DE (vs the full load of 6) in case I had somehow inadvertantly added too much last time

Today we have exactly the same problem again with poor flow. PSI has already risen by 2. On Recirc everything looks normal. Water is getting cloudy

Next step I guess is to disassemble the filter and clean again. Any other suggestions ? Do I need to acid-wash the grids? I'm relatively new to this so all help gratefully received

Andy

30,000 gallon Concrete pool
Pentair SVRS pump
Pentair FNS 60 DE filter
SWG

 

[Bama Rambler]

What you have is the beginnings of an algae bloom. That's what's clogging your filter so quickly. Post a full set of test results and how you got them.
pH
FC
CC
TA
CH
CYA
Salt.

You're going to need to shock but in order to know what your shock level is you need to know your CYA (stabilizer) level.

 

[JasonLion]

Welcome to TFP!

What speed are you running the pump at? At lower speeds the pressure won't go up as much before the filter needs cleaning.

DE filters catch a lot of debris. If the water is cloudy/murky this would make total sense. But if the water is clear and has been for some time it is much more difficult to explain.

Don't acid wash the grids unless there is obvious calcium scaling on them, and even then do an overnight soak first. You need to clean the grids when the pressure right after a through tear down and clean out is higher than it should be. If so, rinse the grids with a garden hose, soak them overnight in a mixture of one cup of automatic dishwasher detergent for every five gallons of water, rinse with a garden hose again, and then reinstall in the filter.

 

[ayouard]

Thanks for the quick response !

Since posting I just stripped and cleaned the grids manually. What I saw is that there was a lot of old dirty DE still there - seems that my backwash yesterday just didnt do a good job. I rinsed and backwashed several times yesterday, but it left a lot of DE behind. As I then added even more DE I may have made it worse. I hope thats all it was.

Anyway, no scaling, so I guess acid wash isnt necessary

I hadnt thought of Algae. Test results below, based on my test with an FAS-DPD kit, and as Im new to this I took another sample to Leslies to double-check my numbers. Only CYA differed between me and Leslies

pH 7.6
FC 2
Total Cl 2
TA 100
CH 350
CYA 60 (me) 100 (Leslies)
Salt 2700 - I plan to adjust this today

What signs would I see in the test results that would indicate algae?

Should I shock anyway? Can I just use the SWG boost fuinction, or should I add some bags of shock?

Thanks again for the input

 

[ayouard]

Forgot to answer this one
Speed is 1900 rpm, fairly low, but we know that keeps it clear under normal circumstances. RUnning lower speeds in the past allowed water to get murky. Water has been clear all the time until the last couple of days since we started having the flow problem

 

[ayouard]

Update on this. We shocked as advised (went up to 25), brushed and ran the pump overnight. Next day pool was a bit more clear. FC was still over 20, but we had white powdery residue everywhere - more reading indicated that was probably dead algae. Weve done several backwashes to keep the flow up and shocked again last night. Clearer again today with more powdery deposits. Vacuumed several times, and manually cleaned off the grids, which were heavily covered with dark gray matter (algae?). Flow is much better, water is clear, so Im hoping a couple more days of monitoring, brushing and maybe backwashing will get us back to normal.

Thanks for the excellent pointer to incipient algae being the cause of poor flow - really helped us deal with it quickly as there was no visible sign of algae, so we wouldnt have found that until it was a bigger problem

 

[tcm]

I have this same filter and one thing to keep in mind is algae or no algae I have found that I need to backwash the filter based more on what my return flow is doing more so then the pressure rise. I have noticed that the return flow is reduced significantly after only about 3 or 4 psi in pressure rise. Don't know if the pressure guage is reading correctly or not, I can only assume so.

 

[ayouard]

Interesting - thats a good tip