Is a pool refill best option in my case?

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Sherlock

Sherlock

Active member
Jun 14, 2023
42
Arizona
I have a 20,000 gallon pool in Arizona.

It uses a cartridge filter (Sta Rite 300 sq ft) that is ancient and due to be replaced on Tuesday 14th.

A few weeks ago a green algae bloom began to appear, and I suspect this was due to unusually rainy weather in Feb/Mar and reduced chlorine because I didn't notice chlorine tabs had gone low.

I brushed the pool surface and wall using a long handled pool brush and added shock, the filter pressure the next day was about 30 psi so clearly the algae was clogging the filter.

I shutdown the system, removed cartridges (which are almost new, installed in Jan or so) and could see green all over them so I hosed them down and got them looking much cleaner.

Restarted the system, saw excellent water flows and pressure 10psi so left it, but a few hours later saw reduced flow and 25psi.
The recently tested water at Leslie's here's that report:

1715521752845.png

This was ten days ago. I did restore the chlorine tabs that day and they've been maintained since then but I'm yet to retest.

I have guests coming in four weeks and want use of the pool, I've been here ten years and the pool has been fine but I did have a pool guy until a year ago, so yes this is my fault I'm sure.

I see two options for resolving this:

1. Clean the filter, put it back, let it clog again and repeat until the concentration of algae is invisible
2. Pump the water out and refill, Leslie's have suggested this several times anyway (last replaced about 4 yrs ago).

Obviously I'd establish good water chemistry right after the refill.

I have no idea how many filter run/clean cycles I need to get rid of the algae if it's like four or five I could do it I guess, but if its lots more then the effort seems to suggest a refill.

A refill has a cost here for me about 1,000 dollars because we are on a well that simply cannot deliver 20,000 gallons in a day so we get it delivered.

I'm also wondering if doing a bunch of run/clean cycles with the new filter is sensible too since it's brand new (its CCP 420 from Pentair).

Thoughts?

Thanks.
 
Sherlock said:
I have a 20,000 gallon pool in Arizona.

It uses a cartridge filter (Sta Rite 300 sq ft) that is ancient and due to be replaced on Tuesday 14th.

A few weeks ago a green algae bloom began to appear, and I suspect this was due to unusually rainy weather in Feb/Mar and reduced chlorine because I didn't notice chlorine tabs had gone low.

I brushed the pool surface and wall using a long handled pool brush and added shock, the filter pressure the next day was about 30 psi so clearly the algae was clogging the filter.

I shutdown the system, removed cartridges (which are almost new, installed in Jan or so) and could see green all over them so I hosed them down and got them looking much cleaner.

Restarted the system, saw excellent water flows and pressure 10psi so left it, but a few hours later saw reduced flow and 25psi.
The recently tested water at Leslie's here's that report:

View attachment 572278

This was ten days ago. I did restore the chlorine tabs that day and they've been maintained since then but I'm yet to retest.

I have guests coming in four weeks and want use of the pool, I've been here ten years and the pool has been fine but I did have a pool guy until a year ago, so yes this is my fault I'm sure.

I see two options for resolving this:

1. Clean the filter, put it back, let it clog again and repeat until the concentration of algae is invisible
2. Pump the water out and refill, Leslie's have suggested this several times anyway (last replaced about 4 yrs ago).

Obviously I'd establish good water chemistry right after the refill.

I have no idea how many filter run/clean cycles I need to get rid of the algae if it's like four or five I could do it I guess, but if its lots more then the effort seems to suggest a refill.

A refill has a cost here for me about 1,000 dollars because we are on a well that simply cannot deliver 20,000 gallons in a day so we get it delivered.

I'm also wondering if doing a bunch of run/clean cycles with the new filter is sensible too since it's brand new (its CCP 420 from Pentair).

Thoughts?

Thanks.
Click to expand...
Welcome! You really dont need to drain the pool
completely, you just need to maintain the correct amount of chlorine. You are way below minimum because your CYA is so high. (Those tablets you use are causing that). Draining half the pool would reduce the CYA by half.

Heres the link for the CYA -FC ratio you need to maintian:
www.troublefreepool.com

The Free Chlorine and Cyanuric Acid Relationship

Managing your cyanuric acid and Free Chlorine levels is key to stabilizing your pool. Learn how these two items affect each other.
www.troublefreepool.com www.troublefreepool.com

But thats only if Leslies test results are accurate and theres only one thing we know for sure and that is Lesies (and any other pool store) dont have a reputation for accurate testing.

Get your own test kit and post up the reaults from that and we can help you out. Until then, you need to be adding 5ppm of liquid chlorine to the pool every day to keep algae from getting worse.

Heres the test kit link:
www.troublefreepool.com

Swimming Pool Test Kits Compared

What pool test kit should I buy? Why not use test strips? Our recommended test kits will pay for themselves in no time!
www.troublefreepool.com www.troublefreepool.com
 
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I suggest you start doing your own testing. This site's proven methods work wonderfully but the cornerstone is owner participation.

The pool store's advice and TFP's advice aren't compatible. We aren't trying to sell you stuff, they are.

For your water, once you test and if your own tests confirm store numbers, I would suggest a partial or complete water change. Primarily because your CYA level is too high. Also your CH is high but I know out where you are this is a problem.

Your filter does not make algae die. Proper water chemistry does. Until/unless you get your water parameters under control, you will always have algae issues.

Pool Care Basics

FC/CYA Levels
 
Bperry said:
Welcome! You really dont need to drain the pool
completely, you just need to maintain the correct amount of chlorine. You are way below minimum because your CYA is so high. (Those tablets you use are causing that). Draining half the pool would reduce the CYA by half.

Heres the link for the CYA -FC ratio you need to maintian:
www.troublefreepool.com

The Free Chlorine and Cyanuric Acid Relationship

Managing your cyanuric acid and Free Chlorine levels is key to stabilizing your pool. Learn how these two items affect each other.
www.troublefreepool.com www.troublefreepool.com

But thats only if Leslies test results are accurate and theres only one thing we know for sure and that is Lesies (and any other pool store) dont have a reputation for accurate testing.

Get your own test kit and post up the reaults from that and we can help you out. Until then, you need to be adding 5ppm of liquid chlorine to the pool every day to keep algae from getting worse.

Heres the test kit link:
www.troublefreepool.com

Swimming Pool Test Kits Compared

What pool test kit should I buy? Why not use test strips? Our recommended test kits will pay for themselves in no time!
www.troublefreepool.com www.troublefreepool.com
Click to expand...
Thanks for a prompt response. So 5ppm in a 20,000 gallon pool would be about how much liquid per day?

I have no problem with a complete drain/refill I'm trying to decide if that's the best way to handle this, or if repeated filter cleans will be enough, I was planning to replace the water next spring.
 
Sherlock said:
Thanks for a prompt response. So 5ppm in a 20,000 gallon pool would be about how much liquid per day?

I have no problem with a complete drain/refill I'm trying to decide if that's the best way to handle this, or if repeated filter cleans will be enough, I was planning to replace the water next spring.
Click to expand...

You need around 1/2 a gallon of 10% chlorine solution per day to add 2.5 parts chlorine, which is about what your pool should be using if water parameters are proper.
 
Sherlock said:
Thanks for a prompt response. So 5ppm in a 20,000 gallon pool would be about how much liquid per day?

I have no problem with a complete drain/refill I'm trying to decide if that's the best way to handle this, or if repeated filter cleans will be enough, I was planning to replace the water next spring.
Click to expand...
Filter cleaning is not your issue and wont do anything.

1 gallon of 10% chlorinating liquid will add 5ppm chlorine to the water. Walmart or home depot carry it.
 
Bperry said:
Filter cleaning is not your issue and wont do anything.

1 gallon of 10% chlorinating liquid will add 5ppm chlorine to the water. Walmart or home depot carry it.
Click to expand...
I understand that the filter alone will not eliminate the algae. The water is cloudy green so in addition to inhibiting further algae growth, I need to get the existing alga out don't I? If I kill all the algae, will the water also clear up or will I still need to remove all that biomass? This is why I'm trying to decide between just repeated filter cleans or simply a refill.
 
Forgot to mention, I do have a testing kit but the included manual is quite a lot of reading. I'm an engineer by training, electronics and software and used to involved stuff, but I'm coming in to this testing, a real green horn!

This is the kit, I never used it because shortly after it arrived I found out about Leslie's free testing.

 
Sherlock said:
Forgot to mention, I do have a testing kit but the included manual is quite a lot of reading. I'm an engineer by training, electronics and software and used to involved stuff, but I'm coming in to this testing, a real green horn!

This is the kit, I never used it because shortly after it arrived I found out about Leslie's free testing.

Click to expand...

That is a very good kit and FAR more accurate than Leslie's. If the kit is over 2 years old, however, I suggest you get a new reagents. TFtestkits.net
 

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Sherlock said:
Forgot to mention, I do have a testing kit but the included manual is quite a lot of reading. I'm an engineer by training, electronics and software and used to involved stuff, but I'm coming in to this testing, a real green horn!

This is the kit, I never used it because shortly after it arrived I found out about Leslie's free testing.

Click to expand...
Assuming your test kit was stored properly, you may be able to get through the season with it. But, you need the Taylor k-1515 FAS/DPD chlorine test kit, which is capable of measuring FC levels up to 50 ppm. Your test kit doesn't include it. Consider a new complete test kit from tftestkits.net. They provide the best value for homeowners.

Even it pool store testing was accurate (it's not), you'll need an accurate test kit at the house. When you SLAM, you'll need to maintain high FC levels, by testing several times a day and adding liquid chlorine. Your best bet is to stay out of the pool store and trust your own test kit.

First, test your CYA with your kit. This will determine whether a water exchange is needed.
 
PoolGate said:
You need around 1/2 a gallon of 10% chlorine solution per day to add 2.5 parts chlorine, which is about what your pool should be using if water parameters are proper.
Click to expand...

OK so I'll get this underway today, I'll buy some of this and start today, this will stop the growth and kill what's already there?

It seems though that my filter is going to clog over and over until the concentration of algae (alive or dead) is greatly reduced, my problem is I don't know how many times I'll need to repeatedly clean the filter in order to get to that point. As I said after cleaning yesterday pressures 10psi but a few hours later was 30psi, so I need to clean it again today (or just wait until Tuesday and start using the new filter but that's will likely clog too until the algae "level" gets low.
 
Rancho Cost-a-Lotta said:
Assuming your test kit was stored properly, you may be able to get through the season with it. But, you need the Taylor k-1515 FAS/DPD chlorine test kit, which is capable of measuring FC levels up to 50 ppm. Your test kit doesn't include it. Consider a new complete test kit from tftestkits.net. They provide the best value for homeowners.
Click to expand...
I should mention that when you SLAM, you'll burn through the FC reagents quickly since you'll be testing high FC levels. Compare reagent bottle sizes when comparing test kits. The .75oz bottles may not be enough to get your through a SLAM.
Sherlock said:
It seems though that my filter is going to clog over and over until the concentration of algae (alive or dead) is greatly reduced, my problem is I don't know how many times I'll need to repeatedly clean the filter in order to get to that point. As I said after cleaning yesterday pressures 10psi but a few hours later was 30psi, so I need to clean it again today (or just wait until Tuesday and start using the new filter but that's will likely clog too until the algae "level" gets low.
Click to expand...
During the SLAM, you'll need to clean the filter each time pressure increases 25% over clean pressure. This removes the dead algae and clears the pool.

Other option is to drain and refill with fresh water. The deci$ion is yours.
 
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I believe you need to go back to the basics.
Read Pool Care Basics
You need to follow the SLAM Process. Likely you will need a drain/refill before that, but you need accurate test results.
To do that, you need a proper test kit. What you have is sufficient if you add the K1515 FAS DPD test. I would also replace the pH indicator reagent.

The pool store tests show great resolution. But the accuracy and repeatability are not good. You are welcome to continue to use them, but we do not provide guidance based on pool store tests.
 
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Sherlock said:
OK so I'll get this underway today, I'll buy some of this and start today, this will stop the growth and kill what's already there?

It seems though that my filter is going to clog over and over until the concentration of algae (alive or dead) is greatly reduced, my problem is I don't know how many times I'll need to repeatedly clean the filter in order to get to that point. As I said after cleaning yesterday pressures 10psi but a few hours later was 30psi, so I need to clean it again today (or just wait until Tuesday and start using the new filter but that's will likely clog too until the algae "level" gets low.
Click to expand...

Yeah - no. This is not what I meant. The key is correct water parameters. Since your CYA is so high (assuming the pool store testing is correct, which it probably is not, but I digress) you need a higher chlorine level. Just based on 130, you should be keeping close to a level of 10-13 (10% of CYA). That is 2-3 gallons a day of 10% chlorine roughly for your pool.

Don't worry about your filter until your water parameters are corrected. Your filter just stores particulate matter from the water column. It has nothing to do with water sanitation.
 
Sherlock said:
OK so I'll get this underway today, I'll buy some of this and start today, this will stop the growth and kill what's already there?
Click to expand...
Adding 5 ppm of FC daily only helps to stabilize things until you get your kit together and start the SLAM.
 

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