Algae help

Afotomama

Well-known member
Apr 30, 2019
46
Daphne AL
Pool Size
8400
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
We are in our second season as aboveground pool owners (Intex Ultra 12x24 SWG). Last year we have beautiful crystal clear water until the end of the season, when we got algae and never could get it back, even following the SLAM instructions here. We ended closing it early. This year we opened it very early and it has been beautiful and clear for a month. But we got busy last week and no one used the pool for 3 days, and it's covered. It rained a few times. And it got hot out. Water temp suddenly spiked and was in high 80s. And apparently my husband turned off the filter for some reason and forgot to turn it back on. I had been checking the chlorine and pH daily.
We very suddenly had a green pool.
When I checked levels, FC was 2.5 and CC .5. CYA was 80 and pH was 7.5. I'm confused about getting algae when we still had good chlorine and pH? I guess with water temps getting high and the water not being circulated and filtered that did it?
We added shock and the next day algae cure. No change. FC now 7.5 but CYA dropped to 35 overnight!
We are getting ready to leave town for a month so I'm freaking out that we will have to leave and come home to an unusable pool.
My neighbor says to add baking soda and CA and wait 3 days. Ideas? Our pool is about 8000 gals.
 

Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
5,357
NW Ohio
I think the issue is your understanding of "good chlorine". The proper chlorine level is a function of the CYA level, per the FC/CYA Chart. If your CYA was 80 then your FC should never have been below 6. It didn't have anything to do with the pH, nor the filter, nor the heat. You just didn't have enough chlorine in your water.

I'm afraid to ask, but what is "algae cure"? I guarantee it's nothing we would have recommended putting in your water.

Baking soda and calcium do nothing regarding algae, I can't imagine why your neighbor would think that at all.

Following the SLAM Process works. Always. There is no reason it wouldn't have last year, there is no reason to think it won't this year. It is not an overnight process, it takes time. And it works, if it is done to completion and you don't try to shortcut it or give up on it early. That's really all there is to it, it's just a matter of patience and perseverance.
 

Afotomama

Well-known member
Apr 30, 2019
46
Daphne AL
Pool Size
8400
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
So... no answer on what "algae cure" is? Because the only product I know by that name is for ponds and would really screw up pool water.
Oh, sorry! Here's a picture:
My husband put one of the pool shock packets in one day and the algae cure in the next day.

So my question is, the CYA was at 80 before we added the pool shock. It lowered overnight to 35 after he added that. To figure out what level to maintain for SLAM, do I use the before or after CYA?
 

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Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
5,357
NW Ohio
Ok, the algaecide is not a very good one, but won't cause major issues. Phew, not what I thought it was! Thanks for posting it.

You can't use that shock, it is dichlor and will add just as much CYA as it does FC. It also contains copper, an algaecide but one you desperately want to avoid. And on the CYA point, something is wrong with those test result. Your CYA would go up after adding that stuff, not down. What are you using to test and how long before and after adding the shock was the CYA tested?
 

Afotomama

Well-known member
Apr 30, 2019
46
Daphne AL
Pool Size
8400
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
Glad the algaecide isn't contributing to the problem at least. Ok so we used the wrong shock. Now to mitigate that, what do I do?
I'm using the TF-100 test kit. We also thought it was wrong that the CYA would change like that, but we both tested and checked and that's what we got. It doesn't make sense. We got CYA 80, added shock, and tested next day and got 35.
Not sure how to proceed...
 

Afotomama

Well-known member
Apr 30, 2019
46
Daphne AL
Pool Size
8400
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
Really need some help moving forward. I read the instructions but am not sure which value to use to know what my SLAM FC level should be. Should I base on the CYA of 80 that we had before we added anything and when we first noticed the algae? Also freaking out a bit because we are leaving town in a few days for a month, and it sounds like I won't be able to get this done by the time we leave. I'm afraid of coming home to a swamp!
 

aeh0603

Well-known member
Apr 6, 2016
353
San Diego, CA
You can get started on the SLAM process using CYA 40, then confirm CYA and adjust your FC target if necessary. Make sure you have plenty of liquid chlorine on hand.

Set your pump to run 24/7 during your SLAM.
Lower your pH to 7.2 and allow at least 20-30 minutes for the pool to mix before you add chlorine. Acid and chlorine cannot be added at the same time.
Add FC (using liquid chlorine or plain bleach) per the chart for CYA of 40 at least 3 times per day. At first you may want to test every hour or two to bring it back to SLAM level. This will speed up the process.
Vacuum your pool as needed (if there is visible debris), brush your pool at least once per day.

Once you have all of the above started, verify your CYA. One of the two numbers is incorrect so you will need to pull a new sample after ensuring the pool is well mixed and test it again. Once you verify your actual CYA level, use that value for your SLAM target moving forward.

Some notes on the CYA test:
1. Make sure your pool pump is on and the water is well mixed before pulling your sample. If you have had a lot of rain and the water is not well mixed, this could cause a false low reading.
2. When you are doing the test, make sure you are outside in full sun. Turn your back to the sun and hold the tube about waist level. Pour a little solution in the tube and glance in. When the dot is no longer visible at first glance that is the end of the test.
3. If the dot disappears between 2 lines, always round up. The scale on the tube is not linear (it's logarithmic) so you can't estimate between the lines.
 

Afotomama

Well-known member
Apr 30, 2019
46
Daphne AL
Pool Size
8400
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
You can get started on the SLAM process using CYA 40, then confirm CYA and adjust your FC target if necessary. Make sure you have plenty of liquid chlorine on hand.

Set your pump to run 24/7 during your SLAM.
Lower your pH to 7.2 and allow at least 20-30 minutes for the pool to mix before you add chlorine. Acid and chlorine cannot be added at the same time.
Add FC (using liquid chlorine or plain bleach) per the chart for CYA of 40 at least 3 times per day. At first you may want to test every hour or two to bring it back to SLAM level. This will speed up the process.
Vacuum your pool as needed (if there is visible debris), brush your pool at least once per day.

Once you have all of the above started, verify your CYA. One of the two numbers is incorrect so you will need to pull a new sample after ensuring the pool is well mixed and test it again. Once you verify your actual CYA level, use that value for your SLAM target moving forward.

Some notes on the CYA test:
1. Make sure your pool pump is on and the water is well mixed before pulling your sample. If you have had a lot of rain and the water is not well mixed, this could cause a false low reading.
2. When you are doing the test, make sure you are outside in full sun. Turn your back to the sun and hold the tube about waist level. Pour a little solution in the tube and glance in. When the dot is no longer visible at first glance that is the end of the test.
3. If the dot disappears between 2 lines, always round up. The scale on the tube is not linear (it's logarithmic) so you can't estimate between the lines.

Thank you. So, don't add CYA (unless it's below 30, and since we are above 30 we are rounding to 40), correct? And for the shock level, you say to use 40. But we have a SWG pool, and the chart starts at 60, so I don't know what the SLAM FC goal is...
 

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Afotomama

Well-known member
Apr 30, 2019
46
Daphne AL
Pool Size
8400
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
Thank you. So, don't add CYA (unless it's below 30, and since we are above 30 we are rounding to 40), correct? And for the shock level, you say to use 40. But we have a SWG pool, and the chart starts at 60, so I don't know what the SLAM FC goal is...
Ok, nevermind, I see that the maintenance levels are different but the SLAM shock levels are the same for both pool types. I'll get FC up to 16 then. Thank you!
 
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aeh0603

Well-known member
Apr 6, 2016
353
San Diego, CA
Thank you. So, don't add CYA (unless it's below 30, and since we are above 30 we are rounding to 40), correct? And for the shock level, you say to use 40. But we have a SWG pool, and the chart starts at 60, so I don't know what the SLAM FC goal is...
Ok, nevermind, I see that the maintenance levels are different but the SLAM shock levels are the same for both pool types. I'll get FC up to 16 then. Thank you!
Correct, the SLAM level target is based only on CYA level (which is why it's important for you to confirm yours), so it doesn't matter if you have a SWG or not. Actually during the SLAM it's usually recommended to turn your SWG off and dose FC manually using liquid chlorine.

The difference in maintenance targets for the two FC/CYA charts (SWG vs manual FC addition) is due to how they are added. With a SWG a small amount of FC is added slowely over time so the actual FC level is much more stable than with manual additions. Both pool types use the exact same sanitizing agent (chlorine) so that's why SLAM level is the same. Salt doesn't affect the FC/CYA relationship.
 

Afotomama

Well-known member
Apr 30, 2019
46
Daphne AL
Pool Size
8400
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
Currently doing SLAM to combat algae. I now understand the relationship between FC levels and CYA, and the SLAM process makes sense, and the Pool Math App is a great help. But I'm still struggling with understanding a few things. Please clarify:

1. When we first noticed the water turning green, our CC level was .5. Now 3 days after initial shock treatment and algae cure (which I now know were both wrong to use), and after a day of SLAM, it's still .5. According to SLAM instructions, a .5 CC level indicates no algae present, correct? So if we know we have algae and we consistently get a CC of .5 over 3 days of readings, what does that mean?
2. Our 8400 gal Intex is supposed to filter the water completely every 4 hours. So if I'm taking readings every 30-60 min, and the water hasn't completely filtered, how can I get consistent results? I'm using the FAS-DPD FC test. Tonight I took a reading from one spot in the pool (after the sun went down) and got FC 16.5, but then a few minutes later from another area (same depth) and not far from the other spot) I got 15! And to make matters more confusing, it had been 5 hours since I'd added any chlorine. So, if the way to tell if algae is present is the overnight test, and if it goes down by 1.0 or less, and I'm getting a difference in readings of 1.5, how will I know when we have killed everything? I don't know how I could possibly be doing the test wrong, it is pretty straight forward, but I guess it's possible that I"m a complete idiot.
The readings from today look like this (CYA 40, so shock level target 16)
11am: FC 5, add chlorine (using pool math app)
2:12pm: FC 17
3pm: FC 15; add chlorine (using app)
4:15pm; FC 17
5:15 FC 16.5
6:15 FC 17.5
8:20 FC 16.5, but when I tested in a different location a few minutes later it was 15. Do I add chlorine or not????

I don't know what I'm doing wrong to get such different readings. Any tips greatly appreciated! We are leaving town in a few days for a month, so I really want to get this under control before we go. Thank you!
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
51,248
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
CC does not imply algae. CC is the byproduct of chlorine oxidizing ammonia based organic compounds. CC is one indicator, not the only indicator.
Chlorine is hydrophillic. It disperses in water quickly. You are thinking that turnover, how long it takes your pump to run through your pool volume, matters. It does not.
FC variation in the column, especially during the time you are adding for a SLAM, would not be unusual. The OCLT is run over night, with no chlorine additions. As you are to run the pump overnight, the FC should be consistent throughout the pool the next morning.
 

Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
23,932
San Dimas, CA (LA County)
Currently doing SLAM to combat algae. I now understand the relationship between FC levels and CYA, and the SLAM process makes sense, and the Pool Math App is a great help. But I'm still struggling with understanding a few things. Please clarify:

1. When we first noticed the water turning green, our CC level was .5. Now 3 days after initial shock treatment and algae cure (which I now know were both wrong to use), and after a day of SLAM, it's still .5. According to SLAM instructions, a .5 CC level indicates no algae present, correct? So if we know we have algae and we consistently get a CC of .5 over 3 days of readings, what does that mean?
2. Our 8400 gal Intex is supposed to filter the water completely every 4 hours. So if I'm taking readings every 30-60 min, and the water hasn't completely filtered, how can I get consistent results? I'm using the FAS-DPD FC test. Tonight I took a reading from one spot in the pool (after the sun went down) and got FC 16.5, but then a few minutes later from another area (same depth) and not far from the other spot) I got 15! And to make matters more confusing, it had been 5 hours since I'd added any chlorine. So, if the way to tell if algae is present is the overnight test, and if it goes down by 1.0 or less, and I'm getting a difference in readings of 1.5, how will I know when we have killed everything? I don't know how I could possibly be doing the test wrong, it is pretty straight forward, but I guess it's possible that I"m a complete idiot.
The readings from today look like this (CYA 40, so shock level target 16)
11am: FC 5, add chlorine (using pool math app)
2:12pm: FC 17
3pm: FC 15; add chlorine (using app)
4:15pm; FC 17
5:15 FC 16.5
6:15 FC 17.5
8:20 FC 16.5, but when I tested in a different location a few minutes later it was 15. Do I add chlorine or not????

I don't know what I'm doing wrong to get such different readings. Any tips greatly appreciated! We are leaving town in a few days for a month, so I really want to get this under control before we go. Thank you!
1) Don't worry about CC until the end. Even if it forms from algae oxidizing, sunlight will destroy it. There are many people who never get a CC reading. Sometimes for no reason at all my crystal clear water shows a tinge of pink that is cleared up with one drop for several days and then it just goes away. We treat .5 CC or less as none.
2) You have poor circulation if you see that much variation in FC around the pool. That may also be why you got algae. Lacking multiple returns, the solution is brushing. So dribble your bleach into the return stream and then brush the pool to get it everywhere as well as to break up the biofilm on any wall-clinging algae so the bleach can kill it. Go brush some more and then take some readings and then decide if you need to raise FC again. And after the pool is clear, brush frequently. It's the most tedious back-and-shoulder-wearing job there is, but it's important.
 

Afotomama

Well-known member
Apr 30, 2019
46
Daphne AL
Pool Size
8400
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
So crazy. CYA reading 80 before adding (wrong) shock. That shock was supposed to make CYA go up, but it dropped the next day to 40. Started SLAM process and at then end of the day CYA was still 40. Continuing SLAM, and now, on 4th day, with no additions besides liquid chlorine, it is back up to 60. I really don't understand, Between inconsistent FC and CYA readings, it's impossible to know how often to add chlorine and to what shock level I should use.
 

aeh0603

Well-known member
Apr 6, 2016
353
San Diego, CA
Ok so I just want to clarify something. Your actual CYA level is not bouncing up and down. What you are seeing is testing variation/testing errors, this is why I recommended verifying your CYA level. CYA does not just disappear from water, if you haven't drained half your pool then half your CYA did not disappear. To lower CYA, you drain water, there is also a very slow degradation over time at a rate of 5-10 per month depending on time of year/water temperature. To raise CYA, you add it either by itself or in combination with chlorine.

If a pool store did any of your readings, I would not trust those values. Pool stores are notorious for incorrect CYA readings.

Some of the biggest sources of error on the CYA test are very cold water temperature (less of an issue this time of year, but for accurate results, the water should not be below room temperature), incorrect lighting (too bright will read a false high, too dark will read a false low), staring too hard at the dot (your mind can start playing tricks on you).

When you are doing the test, make sure you are outside in full sun. Turn your back to the sun and hold the tube about waist level. Pour a little solution in the tube and glance in. When the dot is no longer visible at first glance that is the end of the test. Note: the test solution can be poured back and forth to re-do the test if you are not sure of your result.

If you are confidant in your new reading of 60 CYA, use that to determine your new SLAM FC target moving forward.
 

Afotomama

Well-known member
Apr 30, 2019
46
Daphne AL
Pool Size
8400
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
Ok so I just want to clarify something. Your actual CYA level is not bouncing up and down. What you are seeing is testing variation/testing errors, this is why I recommended verifying your CYA level. CYA does not just disappear from water, if you haven't drained half your pool then half your CYA did not disappear. To lower CYA, you drain water, there is also a very slow degradation over time at a rate of 5-10 per month depending on time of year/water temperature. To raise CYA, you add it either by itself or in combination with chlorine.

If a pool store did any of your readings, I would not trust those values. Pool stores are notorious for incorrect CYA readings.

Some of the biggest sources of error on the CYA test are very cold water temperature (less of an issue this time of year, but for accurate results, the water should not be below room temperature), incorrect lighting (too bright will read a false high, too dark will read a false low), staring too hard at the dot (your mind can start playing tricks on you).

When you are doing the test, make sure you are outside in full sun. Turn your back to the sun and hold the tube about waist level. Pour a little solution in the tube and glance in. When the dot is no longer visible at first glance that is the end of the test. Note: the test solution can be poured back and forth to re-do the test if you are not sure of your result.

If you are confidant in your new reading of 60 CYA, use that to determine your new SLAM FC target moving forward.
My husband and I have each performed the tests separately and both are getting the same readings. I get that the CYA amount isn't changing. But our methods when testing seem to be correct and consistent, thus my frustration with all of this because the action we are supposed to take changes based on our inconsistent test results. That said, we got 60 again and are using the new SLAM level.
 

Afotomama

Well-known member
Apr 30, 2019
46
Daphne AL
Pool Size
8400
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Intex Krystal Clear
(Almost) off the subject, but who is going to manage your pool in your 30-day absence?
That is the problem. We planned on the neighbors checking in on it but they don't have time to maintain this process. I'm running out of time. This morning we still saw a drop from FC 24 last night to 14. So I'll try to keep SLAming through tomorrow and then I don't know what to do when we leave. I guess we'll come back to a swamp. At this point I almost wonder if we.should drain it and start over when we get back.
 

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