Help With Ongoing Green Pool Water

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R

RobRM

0
Jun 14, 2015
11
Clearwater
Thanks for taking my question. The pool is 17k gallons, plaster, in FL with a cage around it. The owner re plastered last year with no problems. Hayward cartridge filter using Unicel filter (only 1 month old C-8409 model number).

Readings as of last night at 6pm:

FC 3.8
pH 7.4
TA 80
CH 300 (FL has hard water)
CYA 30
No metals - on city water
I'm filtering 24/7 and spraying the filter out every 12 hours.

I use the Taylor k-2006 kit and have compared my tests to the pool store in the past. Reagents are from this year. Brand new bottle of R-0871. Yes, there is a pool store that actually does the tests correctly. Each time our test results are nearly identical.

The issue is ongoing green algae. The water keeps getting a green tint to it. When I sweep it clouds up into a little green cloud. Last night I used 2.5 gallons of liquid chlorine. This morning at 9am I sprayed the filter out. The FC was very high, at least 15ppm. I stopped counting the drops after I hit this number. The r-0871 bottles are a bit expensive. The water sample was still bright red/pink color which leads me to believe the FC was at 20ppm, or possibly higher. The FC held very well. It didn't bottom out at all.

This has me very confused. I understand shock is maintaining a FC of 10 - 12ppm to kill the algae. I use no floccs, clarifiers, phosphate removers, etc.

I thought having the FC up that high would definitely kill the algae but it doesn't. The water did clear up a bit but when I swept this morning there still was a slight green on the edge of the steps. I swept the floor and it was like I never swept or vacuumed the day before. Algae just came right back.

A couple weeks ago the CYA was low and I used about 2 lbs. of trichlor. The CYA was about 20ppm on the K-2006 kit. The CYA was about 40ppm after the trichlor and the water looked perfect with all of the other readings in order. I maintain the FC of 2 - 4ppm. When the FC got to 3.8ppm this time is when the green started back. We get lots of rain in FL right now and with the splashing out and topping off the CYA never really gets about 50ppm.

Please help as I'm stumped on what to do next.

Thanks
 
Hi Rob,
Welcome to TFP!

we dont like to use the word shock here, because that can mean so many different things to so many different people.

You can rid your self of the algae by MAINTAINING FC at SLAM level. the SLAM FC (as well as maintenance) is dependent upon your CYA.
Its a percentage factor of 40%. So with CYA of 30, your SLAM FC is 12.

The SLAM is not a one time proeces. You to MAINTAIN that SLAM FC until all the algae is killed off. The process takes a while. How long depends on lots of factors.
But it DOES work. The Key is to bring FC to SLAM level, test every couple of hours and add liquid chlorine to bring it back up. The more often you can test and keep the FC at SLAM, the quicker it will go.

Once the algae is vidibly gone, and your CC are less than .5, and you pass the overnight chlorine loss test, and your pool is crystal clear, then only then can you bring down the FC to maintaince level.

Pool School - SLAM - Shock Level And Maintain
Pool School - Chlorine / CYA Chart
 
Thank you. I understand maintaining a FC of >12ppm does work. I've cleared up a couple of pools for neighbors and have always done that, BUT, it seems this pool is an anomaly. One pool went clear (not balanced nor did it have FC) but it did go clear with a DE filter. I then added 2 gallons of chlorine and it was good. Another 17k gallon pool just required one dose of chlorine at 2.5 gallons and it was perfectly clear the next day. The FC did drop to 5ppm after 8 hours of filtering so I dosed the pool again up to 12ppm.

As was said, this pool is not following that pattern that I've done about 5 times already. That's why I posted the question.

What I'm hearing you say is that there could still be some visible slimy algae on the steps and floor even though the FC was at 3.8ppm, then I added 2.5 gallons which brought the FC up to at least 20ppm for 12 hours? is that correct? Should I just keep filtering, spraying every 10 - 12 hours, and test the FC tonight? I seriously doubt the FC will be below 12ppm. It's very high right now. Can the residual FC that's already in the pool, and it stays about 12ppm, would be enough to kill the algae? That's the big question.

Thanks
 
Rob,
the answer to your questions is yes. It is possible to have some visible algae that seems to not be effected.
Some algae grows a bio film over it that seems to shield it from the chlorine. Its important to brush the pool so that the biofilm is roughed up and the chlorine can get to the algae

RobRM said:
Thank you. I understand maintaining a FC of >12ppm does work. I've cleared up a couple of pools for neighbors and have always done that, BUT, it seems this pool is an anomaly. One pool went clear (not balanced nor did it have FC) but it did go clear with a DE filter. I then added 2 gallons of chlorine and it was good. Another 17k gallon pool just required one dose of chlorine at 2.5 gallons and it was perfectly clear the next day. The FC did drop to 5ppm after 8 hours of filtering so I dosed the pool again up to 12ppm.

As was said, this pool is not following that pattern that I've done about 5 times already. That's why I posted the question.

What I'm hearing you say is that there could still be some visible slimy algae on the steps and floor even though the FC was at 3.8ppm, then I added 2.5 gallons which brought the FC up to at least 20ppm for 12 hours? is that correct? Should I just keep filtering, spraying every 10 - 12 hours, and test the FC tonight? I seriously doubt the FC will be below 12ppm. It's very high right now. Can the residual FC that's already in the pool, and it stays about 12ppm, would be enough to kill the algae? That's the big question.

Thanks
Click to expand...
 
Got The Pool Cleared But Found New Problem

Hello again and thanks for taking my question. First my current readings:

FC 7ppm
CC 0.0
pH 7.4
TA 80ppm
CH 280ppm
CYA 40ppm

This question is a continuation of the last post I made, for the same pool. The CYA was down to 10ppm so I used 50 oz. of dichlor, filtered for 3 days and the pool finally cleared. The CYA jumped to 40ppm and has been there ever since. At that time the FC was about 15ppm. 2 days later it was at 14ppm. The FC held very well, over 12ppm for at least 5 days. I used the K2006 kit and have been for many years and only use liquid chlorine.

The issue is this. In about 10 days the FC has dropped to 8ppm and now the algae is starting back up again. This is confusing because I've always run the FC around 3 - 5ppm with no problems but this pool seems to be producing algae when the FC levels are even higher. Could this be a sign of the chlorine having less strength? Should a PolyQuat 60 be used?

The pool is a friends and she said she's never had any issues in 13 years. But, what she did was simply pour 2.5 gallons of chlorine in the pool Sunday night and use a bottle of PQ60 each month, rarely testing the water. I think the reason she never had any issues is because she kept the FC up to 10ppm or >. I don't want to keep the FC up that high on a continuous basis but I'm thinking I have no choice.

Thanks for any input.

Rob
 
Re: Got The Pool Cleared But Found New Problem

Hello Rob. Your "First my current readings" above look quite good, and the FC is at a good level compared to the CYA. But what we don't know is if the FC was always that way in the past 1-2 weeks. For example, you mentioned in the post that you've always run a 3-5 FC level. That's bordering on the low-end for a CYA of 40, and anytime the FC got to 3, you're rolling the dice with algae. Especially in FL with all the sun, heat, humidity. In any case, if the pool has algae, it is time to SLAM. The SLAM link is below in my sig, but here's the basics in case you haven't done it in a while:

SLAM is the term used when we “Shock” our pool to a higher “Level” of Free Chlorine (FC) and “Maintain” it that way until 3 objectives are met:
1. Water is clear
2. You do not lose any more than 1ppm of FC overnight (that's the OCLT)
3. CC (Combined Chlorine) is <.5
** You MUST meet ALL 3 items above to properly do a SLAM. Simply “spiking" the FC higher than normal isn't SLAMming, therefore there’s a good chance your algae will return.

To prepare for a SLAM, you should do the following:
- Adjust PH to 7.2 - 7.5; don’t worry about it after that during the SLAM
- Ideal CYA should be 30; the higher the CYA, the more bleach required
- Have a good amount of “regular” liquid bleach on-hand to keep your FC high at all times

Use the Chlorine/CYA chart (link in my sig) to bring your FC up to the proper SLAM level rating based on your current CYA and make sure it stays there (MAINTAIN) until you meet ALL 3 criteria listed above! That may take just a few days or even a week or two! That is absolutely critical for success.

At the same time, continue to run your pump 24/7. Remove any “muck” and debris, scrub all parts of your pool to expose any algae, and vacuum/clean (or backwash) filter as necessary. You may have to do this several times. It's a lot of babysitting, but with patience and consistency, you will succeed.

If the CYA is still at 40, then your SLAM FC level is 16. I would bump it up right away until you meet the 3 requirements above, then make sure the FC never drops below the target (5). AT night, consider adding enough chlorine to not only sanitize and replenish the FC in the pool during dark hours, but to give you enough wiggle room during the day so it doesn't drop below 5. Perhaps shoot for a nightly target of about 9-10.

- - - Updated - - -

And as a reminder to your concern about the chlorine level.... as long as your FC correlates to your current CYA as found on the Chlorine/CYA chart (link below), it is safe for you and your pool.
 
Re: Got The Pool Cleared But Found New Problem

Thanks. It makes sense and that's what I've been doing. The question isn't about the process of maintaining the FC to kill the algae, it's having a CYA of 40ppm (in range) and when the FC dips below 7 - 8ppm the algae starts to appear. My daughter went swimming a few days ago when the FC was about 10ppm and her hair was "crispy" when it dried. Never had that before. I originally got the FC up to about 20ppm with the dichlor and about 1.5 gallons of liquid chlorine. The next day I stopped counting the drops after 18ppm FC and the sample was still bright red. R-0871 drops are $10 a bottle - little expensive.

The question is why would algae start to form on the walls and floor when the FC is still at 7 - 8ppm? Do I need to keep the FC up at 10ppm? That's what it seems to take to keep the water clear? Or perhaps the answer is in your post but somehow I'm missing it.

Thanks
 
We're both in fairly hot/sunny climates. The water takes a brutal beating. When my CYA was at 40, I never let the FC drop below 5, and usually had a personal target of about 7 during the day to be safe. At night I added my bleach with a slightly higher target (say about 10) to ensure anything that burnt-off during the day never went below my target FC. Today, I'm trying for a CYA of at least 50 for more FC protection.

Now having said that, the Chlorine/CYA chart was developed so that the FC and CYA "balance" each other for optimal performance - both in safety and sanitation. As long as any previous algae was completely cleared (SLAMed), then maintaining an FC of 5-7 should be just fine with a CYA of 40. Keep in mind that swimming and other environmental factors/debris can cause more stress on the water using-up FC quicker.

Typically in our experience, if algae returns for any reason, it's either because a previous SLAM ended prematurely, or the FC level dropped too low during the day without the pool owner's knowledge. It doesn't take long or have to drop too low before you start to see the signs.

But if your FC corresponds to the current CYA on the Chlorine/CYA chart, there should be no ill-effects on the swimmers or their hair.
 
Just following along here, you seem to ask a number of times how FC at 7-8 PPM with CYA of 40 allows algae to grow. Logic says it can't based on everything the chem experts are saying. So maybe your readings are wrong? Maybe CYA is higher than 40 PPM or the FC reading is wrong. Maybe have someone else do the test for you maybe with their kit.
I completely messed up my CYA test once (was used to doing the dilute test and spaced on the standard test). I also put my cartridge filter back together wrong once also.
It did not work effectively. When results seemingly defy the norm I check my method. Not insinuating you made a mistake but it is worth it to review your method as a long shot to help fix your problem.

And as mentioned earlier, those of us in sunny climates may benefit from slightly higher CYA levels and the corresponding higher FC levels. Mine was almost 200 PPM CYA two years ago got it down to 60 and in Arizona that seems to work well at 7-10 PPM FC. 330 days +/- of sunshine a year, and 100-110 degrees for most of June and even July and August.

BTW, I ran my pool at 15-18 PPM for a year when CYA was high and never had an issue swimming in it
 

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Re: Got The Pool Cleared But Found New Problem

It's coming back because your not Maintaing the slam to effectively kill off the algae. Until you do that and pass the tests mentioned it will continue to keep flourishing as its already established.

Just keep it up to what was mentioned and test it will go away in time of you do. My fc is at 5 and cya 40 swg pool and it's crystal clear. The level isn't the issue its that you haven't killed off the algae
 
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