Does Poor Filtration CAUSE a Green Pool/Algae Outbreak

Mddan2474

Member
Jul 16, 2020
5
Philadelphia suburbs
Hey All,

Looking for some help in regards to an algae bloom that we just can’t seem to kick.

Some background:

We have an approx 28,000 gallon inground pool with sand filter. This is our 5th summer in this home with this same pool/filter setup. Usually once or twice per summer we have gotten algae issues but have always solved them by shocking the pool, sometimes to very high levels (30 ppm per chlorine) but always with a return to normalcy afterwards.

This year we hit an algae issue towards the end of June that still hasn’t been fully resolved 3+ weeks later. The initial issue, we believe, was that the CYA was too high (130 as measured by Leslie’s) so our shock wasn’t working. We went through a regimen of draining and refilling to get our CYA down (80ish) and then shocked again using a 73% hypochlorite powder shock. Over the course of 36 hours we used 12 lbs of this shock. The pool lightened slightly but never lost the green color. In our previous experiences shocking algae to a high chlorine level turned the pool an opaque bluish white within hours as long as we brushed well. Then our filter would gradually filter it out.

So, after unsuccessfully trying on our own to resolve the green pool we brought out a local pool company to attempt to fix. They got the pool to turn that bluish white opaque color that we had previously seen and we’ve been running filter 24/7 and backwashing and brushing daily. On Monday of this week the pool looked like it was on the right track. Still cloudy but we could actually see the drain in the deep end (9 feet). But by yesterday (Wednesday) we noticed a tinge of green and we cold no longer see the drain and after calling local pool company we shocked with 3 lbs of 73% hypochlorite. This morning, no change, perhaps slightly more green. One thing to note the free chlorine was approx 5ppm on Wednesday when the pool started to turn green, so it was not a simple low chlorine issue that started a new algae issue.

After a follow-up call with the local pool company (whom my impression is that they aren’t swindlers, but you never know) they said they thought that our sand filter is not up to snuff, and they think we should replace it with a 48 or 60 SQFT DE Filter. I am skeptical. One, we had the same setup for four years (and assume the previous owners of house had it for long time as well), our pump and plumbing seem to be in great shape. The only real change this season from last was a tree removal that allows the pool to get more sun. Our filter seemed to work fine for the last four years (and I even changed the sand two years ago), so to say the filter is the issue seems off to me. Additionally I will add that in previous years after killing the green and getting the algae to die and turn bluish white it did take 4-5 days to get a nice crystal clear water. So perhaps the filter doesn’t work as well as it should, but my question Is as follows: If the filter is not filtering out the dead algae at a quick rate will that be the CAUSE of a new algae outbreak? In other words does dead algae increase the chance of getting new live algae? I feel like it is a pool chemistry issue and not a filtration issue, but said pool company is trying to sell me on a new filter.
 

DorsalSpine

Gold Supporter
Silver Supporter
Jul 8, 2013
719
Columbus, Ohio
You need to start with a good test kit and read the Pool School here on the site. If your CYA is really 80ish your chlorine level is too low. Your minimum FC at that level is 6 and your suggested level is 9 - 11. It sounds to me that you didn't keep your FC level high enough.

Most of us don't trust pool store testing (with good reason). Having your own test kit will let you control the outcome. You need to get your CYA level down to the 40 range (assuming you don't have a salt water pool). The ABC's of water chemistry, testing and all that good stuff is in Pool School.
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
23,932
San Dimas, CA (LA County)
Does Poor Filtration CAUSE a Green Pool/Algae Outbreak? No.

Algae is caused by insufficient chlorine for your CYA level. You might think 30 FC is astronomical, but if you've been feeding the pool a steady diet of trichlor pucks and doing a weekly "shock" with dichlor, 30 FC may only be barely adequate for sanitation, and nowhere near enough to get ahead of an algae bloom. Seriously.

 

Dtkokay

Well-known member
Dec 31, 2019
383
Houston, Texas
Your post is missing a crucial piece of information: What level of FC (Free Chlorine) have you been maintaining? Your FC level needs to held at a higher level as your CYA goes up. With your high CYA, your FC needs to be well above the “pool store” recommendation of 1-4 ppm.

Unfortunately, your experience is like 95% of the new people who seek guidance on this forum. Algae problems due to high CYA and low FC. The short answer is to buy a quality test kit, like the TF100 (also get the Speed Stir accessory), so that you actually know where your water quality is at. Then post the results here and folks will give you guidance.

My prediction is that you’ll need to drain to get your CYA down to 50 or less, then SLAM using liquid chlorine. Stop using any kind of shock because it adds other stuff to your water that you probably don’t want. Typical shock includes CYA, which you already have too much of.
 

Griswald

Well-known member
Jul 7, 2014
758
Hope Mills, NC
Thanks for all your input. Sounds like we may need to lower CYA more. I will definitely look into a quality test kit as well.
You are not understanding...yes, you need to lower your CYA, but adding shock and pucks RAISES your CYA.

You lucked out for a few years, like everybody else has, but it eventually catches up with you.
If you want to follow the TFP method ( which is free) fine, but you cannot rely on pool stores (that make money because of your bad water) at the same time. It's all or nothing.

And your sand was millions of years old when you put it in the filter, so how can a few years "wear it out"? Another money maker for the pool store.
 

PoolNewb2020

Well-known member
May 7, 2020
303
Lathrop, CA
You have algae plain and simple. Per your statement, you had to deal with algae right from the beginning, but the difference this time is that you have a much bigger outbreak and a much higher CYA level. Hence the old routine no longer works.
Take a look at the results members of this forum get using the TFP method. The difference should be quite "clear"

TFP clear pools
 

Mddan2474

Member
Jul 16, 2020
5
Philadelphia suburbs
You are not understanding...yes, you need to lower your CYA, but adding shock and pucks RAISES your CYA.

You lucked out for a few years, like everybody else has, but it eventually catches up with you.
If you want to follow the TFP method ( which is free) fine, but you cannot rely on pool stores (that make money because of your bad water) at the same time. It's all or nothing.

And your sand was millions of years old when you put it in the filter, so how can a few years "wear it out"? Another money maker for the pool store.
 

Mddan2474

Member
Jul 16, 2020
5
Philadelphia suburbs
Whoa! Come off strong much? I am understanding. In fact I was the one who was skeptical of the advice that I was getting in regards to the filtration causing the issue and that is WHY I made the original post. And yes, I am a relatively new pool owner, but I have beaten algae blooms previously and have done my own testing previously. This one has stumped me and it seems like it’s probably because I was lied to by the pool store as well as a separate pool company.

My guess, after advice from less condescending TFP members like Richard320, is that my CYA was still too high when it was around 80 to start fixing the problem. I should have continued draining and filling to get it in the 30-50 range. I was given poor advice from two separate pool entities and I won’t make the same mistake again.

I have a question for you as well as other more experienced pool owners. Obviously pool stores will lie and or tell half truths to try to get you to buy their products. But do they actually fudge the numbers that come out of the computer in regards to your water readings? 5 years ago the pool store I went did the old fashioned titration methods and the kid behind the counter seemed to be going fast, almost winging it and I didn’t really trust his numbers. But now the same store just throws the water into a machine and it spits out numbers. Are my measurements from a quality test kit going to be more reliable than those numbers? Perhaps I trust technology too much, but I would think that their numbers should be more accurate, unless they are facts straight manufacturing those numbers to sell you unneeded chemicals. Thoughts?
 

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Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
23,932
San Dimas, CA (LA County)
But now the same store just throws the water into a machine and it spits out numbers. Are my measurements from a quality test kit going to be more reliable than those numbers? Perhaps I trust technology too much, but I would think that their numbers should be more accurate, unless they are facts straight manufacturing those numbers to sell you unneeded chemicals. Thoughts?
The machines are no more accurate than titration and probably less-so. It's my understanding they need to be calibrated and that doesn't happen as often as it should. If the machine prints out the results, there will be no fudging. If someone had-writes them, they might, especially if they know the machine is out of whack, and don't want to try explaining how come the CYA is sky high when only last week they sold you some because it was too low.

Once you get used to doing your own testing you will never go back. You will get to know your pool well, and be able to predict the test results with amazing accuracy before drop one leaves the bottle. And if ever something doesn't make sense -- like CH suddenly dropping and there hasn't been any rain -- you will be able to repeat the test immediately and see what's going on. The pool store will just report it as tested and sell you some calcium increaser.
 

mariane

Bronze Supporter
LifeTime Supporter
May 8, 2012
1,098
Southeast Michigan
Several factors could cause the numbers to be off: (as Richard320 said) the calibration of the machine, whether the clerk rinsed out the previous test water from the container, how accurate the tester put in the numbers, whether the tester was accurate with the size and capacity of your pool, whether the water you took in sat in the hot car or on the counter for a period of time before the testing, etc. :salut:
They just read you the numbers and tell you what you need ie. pH is too high, put in pH Down, FC is too high put in chlorine neutralizer, CYA should be 110 add xx amount of Stabalizer, pool is slightly clouding put in 3 bags of shock, you have phosphates so you need to add . . . you get the idea. They are not trying to scam you. They think they know what they're doing because that's what the readout shows. :deal:
Many factors that are not the case when you test it yourself. You can be pretty accurate with your own testing. :cool:
You put the numbers in Pool Math and it lets you know how much of what to add, stuff that you get at the grocery or hardware store. Easy peasy.
Almost all of use have been in the same situation as you - wanting answers the pool store readout does not give or given solutions that do not work. :hammer:
 

PoolNewb2020

Well-known member
May 7, 2020
303
Lathrop, CA
In my view it is not really relevant because pool store business model revolves around pool owners coming in for testing and leaving with a product sold there. Stores have no vested interest in accuracy of the test, just the appearance of it. They won't send their loved ones to swim in that water anyways.
 

DorsalSpine

Gold Supporter
Silver Supporter
Jul 8, 2013
719
Columbus, Ohio
Our local tool rental place sells pool supplies. He is the one that told me I needed a better test kit when I was fighting a high CYA problem. After that I found TFP and never looked back. I don't trust the pool store that got me into a high CYA problem in the first place. I no longer do business there, despite their high tech machine.

Why do I trust the local rental guy instead? Because his numbers match mine! There isn't a better solution than trusting your own testing.
 

Mddan2474

Member
Jul 16, 2020
5
Philadelphia suburbs
Thanks, everyone for your replies. I never thought that the pool store had my best interest at heart, I just was curious as whether to trust the numbers that came out of the machine when they tested my water. Like I said I have used Taylor water testing kits before, and I feel like it certainly Is a skill. Consistently getting your drops the same size, etc. But it seems like the majority of experienced pool owners still would rather trust their manual efforts than the technology that comes from the pool store. So I’ll work from there. Thanks!
 

PoolNewb2020

Well-known member
May 7, 2020
303
Lathrop, CA
I don't think anyone here has a problem with the tools pools stores use, with the exception of the ones using test strips. Some stores have electronic machines, some use the same Taylor kits we use. The proper tools are not the problem, but the people that are using them and their training.

The root cause is because they don't care about test result accuracy and their business model doesn't have to care.
 
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JoeSelf

Gold Supporter
Jun 18, 2014
759
Glassboro, NJ
To help you trust your numbers consider the Speedstir & Sample Sizer along with the TFT-100 ( Best Bang for your buck). The Samplesizer makes it easy to get repeatable water sample sizes. Speedstir makes it easier to add drops and count. I misplaced my first ones over a winter four years ago. Found them later after replacing them. I now have two of each that's how much I value their worth.
 
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