Flow under 10 gpm in Filter mode vs 50 gpm in backwash

[Joberg]

Hey everyone, we haven't used our equipment during the winter, and recently moved it to a different location closer to the pool. We use all Pentair products (IntelliConnect, Mastertemp, IntelliFlo, etc.). I'm debugging a problem where the pump couldn't prime (half of the basket was filled with water), but the pool maintenance guy would say that it's normal since the pump is higher than the level of the pool. I didn't believe them as I saw examples of pool pumps 8-10 feet above pool level working just fine (mine is 2-3 feet above pool level). So I looked for air leaks on the suction side (inspected all connections with shaving cream), and I didn't find any. I was pretty bummed, and decided to backwash the pool and realized that the pump primed right away (under 10 seconds), and the flow goes up to 50+ gpm. There's only the Mastertemp between my filter and the return line, so I suspect something is up between my filter and/or the heater. I'm pretty new to troubleshooting those types of issues, and I would like to pick people's brains on what type of tests I could do to further diagnose this problem.

 

[mknauss]

Welcome to the forum!
Sounds like your filter is dirty. What type of filter is it? What are your water chemistry results?
I suggest you read ABC's of Pool Water Chemistry.

 

[Joberg]

Welcome to the forum!
Sounds like your filter is dirty. What type of filter is it? What are your water chemistry results?
I suggest you read ABC's of Pool Water Chemistry.

It's a Pentair Tagelus High Rate Sand Filter TA-60/60D. I did a few backwash + rinse cycles, anything else I could do to clean it up? Also note that I can hear bubbles in the heater. The water PH is between 7.4 and 7.6, and the total alkalinity was around 80-100ppm. I didn't do hardness test (I just bought a more sophisticated test kit).

 

[mknauss]

A full set of test results. With FC, CC, and CYA.
What does your water look like?

Any pool store potions put through the filter (floc, phosphate remover/clarifier)?

 

[Joberg]

A full set of test results. With FC, CC, and CYA.
What does your water look like?

Any pool store potions put through the filter (floc, phosphate remover/clarifier)?

No pool store potions unless they dunked it in without my knowledge, I have a chlorine feeder and UV light pool sanitizer, and I've been shocking the pool weekly (that's pretty much it). Every few months I ended up having to clean my filter cartridges manually, they were filled with a thick gray substance. I got tired of it and replace my filter with a sand filter so I could just backwash (must faster). When I backwashed this week, I could see the same gray-ish substance coming out. Anyway, I'll reply once I receive the FAS-DPD kit so I can share proper test results. If there's anything I could do in the meantime to clean the filter then please let me know, thank you!

 

[mknauss]

With the chlorine feeder and weekly shock method, it is very likely you have persistent algae. The gray substance is dead algae.
Keep backwashing as needed and read up on the SLAM Process. I suspect you need to follow it once you get your proper test kit.

 

[Joberg]

With the chlorine feeder and weekly shock method, it is very likely you have persistent algae. The gray substance is dead algae.
Keep backwashing as needed and read up on the SLAM Process. I suspect you need to follow it once you get your proper test kit.

I got the test kit and ran it, here's the data from it below. Now I realize I need to read the chemistry booklet, as this is a bit more complicated than I thought I'll read it tonight.

Here are the test results:

Water temperature: 69/70
Pool size: 19-20k gallons
FC: 1-2 ppm (not kidding)
TC: 1-2 ppm (again, not kidding)
PH: 7.4
Acid Demand: 0
Base Demand: 1 drop
TA: 60-70ppm
CH: 350-360 ppm
CYA: 38-40 ppm
Saturation index: -0.2

 

[mknauss]

Your results should not be ranges. The FAS-DPD test gives definitive FC level to 0.5 ppm. I assume you have a K2005. Is that the kit you have?
It will not work to perform the SLAM Process

When you get a FAS-DPD test for FC/CC, you can do an Overnight Chlorine Loss Test

 

[Joberg]

Your results should not be ranges. The FAS-DPD test gives definitive FC level to 0.5 ppm. I assume you have a K2005. Is that the kit you have?
It will not work to perform the SLAM Process

When you get a FAS-DPD test for FC/CC, you can do an Overnight Chlorine Loss Test

Yea I did K2005, and I put ranges because I had to eye-ball a bit... The K2005 has guidance to do FAS-DPD, but the bottles are missing. I just ordered the K2006. Fun time!

 

[mknauss]

You only need the FAS-DPD test kit. Plus the R0013 reagent refill.

 

[Joberg]

I'm curious, if my pump can barely push 8-10 gpm due to filter clogged with algae residues, will SLAM be effective? At this rate, it will take 33h just to go through all the water in the pool once. Could I do anything to unclog that filter so I can SLAM properly?

 

[mknauss]

What type of filter do you have? Please fill out your signature. It helps us help you.

 

[Joberg]

What type of filter do you have? Please fill out your signature. It helps us help you.

I updated my signature to reflect my system. My filter is Pentair Tagelus High Rate Sand Filter TA-60/60D, pump is Pentair intelliflo VSF, heater is Pentair Mastertemp 250, and UV light is UltraUV2.

 

[mknauss]

Please add the information to your signature block. See my signature for examples. If on a phone, turn it sideways to see our signatures.

Sand filters do not plug off that quickly. Something is wrong with the sand. I suspect phosphate removers or clarifiers have been used in the past.
You should do a Deep Clean of the sand filter. See Deep Cleaning a Sand Filter

 

[Joberg]

Please add the information to your signature block. See my signature for examples. If on a phone, turn it sideways to see our signatures.

Sand filters do not plug off that quickly. Something is wrong with the sand. I suspect phosphate removers or clarifiers have been used in the past.
You should do a Deep Clean of the sand filter. See Deep Cleaning a Sand Filter

Thanks for the article, it's very instructive and helpful. The videos are simple and effective.

One question came up as I read this: when I set my filter to 'recirculate', it should completely bypass the filter, at least according to the article. So when I use that setting on my system, the flow is still 9-10 GPM (instead of 40+ GPM). Given that, would this indicate that the flow problem is 'after' the filter somewhere on the return, between the connection with the heater, inside the heater, or between the heater and return to the pool? Don't get me wrong, I'll do a deep clean of my filter. However, something tells me that the issue might have to be with the heater, or just insufficient flow in the line going back to the pool. Does that make any sense? If so, any other things I could try out to ensure the flow is fine 'after' the filter?

 

[mknauss]

I wonder if the issue is the MPV. Read MPV Valves - Further Reading

 

[Joberg]

I did the FAS-DPD test, 2 drops at 10ml gave me FC at 1ppm and CC at 0ppm.

I didn’t deep clean my filter but I opened up the multi valve, everything seems fine, see pictures attached.
The interesting part is my pressure valve shows no pressure. I removed and re-screwed it in, still no luck, so I ordered a new one just in case it’s broken (no water / air leak that I could see though).

 

[Joberg]

Looking at more examples of the gasket, doesn’t it look thin/weird? I bought a replacement part on Amazon for $30 (the gasket is glued in on those models), I’ll inspect what a brand new gasket looks like, and I’ll just change it if it looks suspiciously different.

 

[sktn77a]

Gasket looks correct and fine. Of course, that doesn't necessarily mean its sealing properly.

 

[mas985]

Do you have any check valves? Occasional they will fail and cause very high restrictions.