Mustard Algae Slam Difficulty

[DT770]

Hello TFP members! This is my third summer of pool ownership and our first SLAM procedure. Carelessly let the FC drop lower than needed for a few days and shortly after started noticing what seems to be mustard algae blooms. Performed a "half-way" SLAM with lower FC levels thinking I could get away with cutting corners and here I am....

SLAM began last Thursday at Ph 7.3 and CYA 50. Progress was going smoothly until today, which was supposed to be the final mustard algae shock level day. OCLT showed a 0.5 FC loss with the morning FC at 19.5.
Around noon, FC was raised to 30, followed by liquid chlorine additions several times throughout the day to keep the FC at 30. Water tests were not performed during the day to save on reagents.

• Testing for FC after 8:00 pm, the result was 17.5 ppm!
• This result is highly unexpected - how can the daytime FC loss be >12.5 ppm after passing the OCLT?

The Pool Math log doesn't show it, but the pool was brushed and vacuumed daily (Ladder was removed and light niche brushed as well). CC readings not recorded as they were not tested for every time; when tested for CC was always 0.0 ppm.
Pool Math Log (Timestamps are incorrect as my time is -4 from the recorded values, although they are shown correctly in the APP)

My R-0871 running thin as each test uses ~40 drops at the necessary SLAM FC level, and even more during mustard algae SLAM! What could be the issue here? Could it be the reagents?

 

[PoolStored]

This result is highly unexpected - how can the daytime FC loss be >12.5 ppm after passing the OCLT?

From Mustard Algae link below: Once you have completed SLAMing your pool in the standard way, raise the FC level up to the extra high mustard algae shock level for 24 hours.

Mustard Algae

Today We are going to show you how you can get rid of mustard algae in your pool. By following the steps in this guide and with no expensive chemicals.

www.troublefreepool.com

This process is no different than the SLAM process. You lost up to 4ppm in 6 hours during your slams, or 16ppm per day, yet that didn't surprise you because you were killing something. Same thing is happening here. You need to TEST and add enough to get back to 30, again every hour is best, or two worst case. My guess is that you are consuming the FC, killing Mustard Algae (if that's what it is), and not replacing enough to get back to 30. You need to do the testing. If you want to save reagent, use 5mL test volume and 1 drop = 1ppm.

Good luck!!! Slam On!

 

[DT770]

From Mustard Algae link below: Once you have completed SLAMing your pool in the standard way, raise the FC level up to the extra high mustard algae shock level for 24 hours.

Yes, that was the intended plan; FC was raised to 30 around noon and maintained for 24 hours. However, FC fell all the way to 17.5 in the span of 8 or so hours.

This process is no different than the SLAM process. You lost up to 4ppm in 6 hours during your slams, or 16ppm per day, yet that didn't surprise you because you were killing something. Same thing is happening here. You need to TEST and add enough to get back to 30, again every hour is best, or two worst case. My guess is that you are consuming the FC, killing Mustard Algae (if that's what it is), and not replacing enough to get back to 30. You need to do the testing. If you want to save reagent, use 5mL test volume and 1 drop = 1ppm.

Good luck!!! Slam On!

I'm surprised because the FC loss seems too high considering that the most recent OCLT was 0.5 ppm FC loss and the one before that 1.0 ppm. If mustard algae was not affected by regular SLAM levels, what could be the cause of high FC loss during this? Pool water is clear as usual and I don't expect any contaminants other than the mustard algae.

As for reagent, 5mL test volumes is what I have been doing, but it is still ~20 drops per test. To try and save even more reagent, before today's final FC test (17.5ppm with 10mL volume) I tested by diluting 1 part pool water with 3 parts distilled water (10mL:30mL). The result with 10mL volume was 4ppm, which was then multiplied by 4 to get 16 ppm. Quite close to 17.5

 

[PoolStored]

I don't expect any contaminants other than the mustard algae.

Which will consume FC. To perform the treatment correctly, you need to test, then re-add enough chlorine to get to 30. The point of the M in SLAM is to maintain. We have no idea if you did that without testing.

 

[PoolStored]

and maintained for 24 hours.

We don't know that.

 

[DT770]

We have no idea if you did that without testing.

Poor wording on my part. FC was raised to 30 and the plan was to keep it at that level for 24 hours. I didn't perform daytime tests and figured one could get away with some frequent chlorine additions, except the FC demand seems to have been much greater.

If the high FC loss during mustard shock was due to the mustard algae, what could cause relative high FC loss during regular SLAM in this case? SLAM was started purely due to mustard algae concerns and no other problems were visible.

 

[PoolStored]

what could cause relative high FC loss during regular SLAM in this case?

TRYING to kill stuff. My OCLT went down for 5 days and then sat for 3 days at 2.5ppm OCLT. I used 45 gallons of Chlorine. Not until I took the ladder out and cleaned it did my OCLT go to 0. Doesn't take much to consume LOTS of FC.

How much algae was in the ladder?

 

[PoolStored]

I didn't perform daytime tests and figured one could get away with some frequent chlorine additions

Nope. Not the way this works. We have 100s of 1000s of pools we have helped. You can't avoid the method and expect success.

 

[DT770]

Nope. Not the way this works. We have 100s of 1000s of pools we have helped. You can't avoid the method and expect success.

As stated in the original post, ladder was removed. Light was removed from niche as well. Only contaminant getting in the pool lately is soil from doing some excavation around our backyard.

I understand the method and what it entails, so testing was performed frequently during regular SLAM. Only today, during mustard slam, did I choose to cut down on testing as the OCLT was successful and I didn't expect rapid FC consumption, where the volume of chlorine added was estimated to be enough to offset this loss.

Takeaway here seems to be that I underestimated the FC loss that would happen once FC was raised to mustard shock levels.

 

[PoolStored]

I understand the method and what it entails, so testing was performed frequently during regular SLAM. Only today, during mustard slam, did I choose to cut down on testing as the OCLT was successful and I didn't expect rapid FC consumption. Takeaway here seems to be that I underestimated the FC loss that would happen once FC was raised to mustard shock levels.

You, my friend, GOT IT. There is a madness to the method method to the madness.

 

[mgtfp]

This result is highly unexpected - how can the daytime FC loss be >12.5 ppm after passing the OCLT?

Chlorine loss due to UV is not a fixed amount but relative to the FC-level.

Let's say you start the day with FC 10ppm and you lose 4ppm, ending the day at 6ppm. That's a loss of 40%.

Now you start the day with FC 30ppm with the same CYA and the same UV-load throughout the day. You will still lose about 40% of your FC (I am not saying that you will always lose 40%, that's just for the sake of this example - but I am sure that there are combinations of CYA-level and daily UV-load where 40% loss would be about right). But 40% from a starting level of 30ppm would be 12ppm.

That's what makes a Mustard-SLAM a challenge - due to the high FC-level you lose a lot of chlorine to UV.

In reality, the total loss will be some combination of UV-loss and loss to the Mustard-Algae you want to kill (and other losses due to FC oxidising things).

 

[DT770]

Chlorine loss due to UV is not a fixed amount but relative to the FC-level.

Let's say you start the day with FC 10ppm and you lose 4ppm, ending the day at 6ppm. That's a loss of 40%.

Now you start the day with FC 30ppm with the same CYA and the same UV-load throughout the day. You will still lose about 40% of your FC (I am not saying that you will always lose 40%, that's just for the sake of this example - but I am sure that there are combinations of CYA-level and daily UV-load where 40% loss would be about right). But 40% from a starting level of 30ppm would be 12ppm.

That's what makes a Mustard-SLAM a challenge - due to the high FC-level you lose a lot of chlorine to UV.

In reality, the total loss will be some combination of UV-loss and loss to the Mustard-Algae you want to kill (and other losses due to FC oxidising things).

I recall reading that somewhere here on TFP but didn't brush up on it before the SLAM, thanks for the refresher!

A 40% FC loss from UV is probably on the extreme end of the bell curve here in Canada, especially given the time frame and our CYA of 50. Most likely the algae added to this loss once the FC was high enough to fight it.
I've seen some posts where daytime FC loss is reported at 2ppm, even 1ppm! Assuming they maintain at a comfortable 8ppm, that's a very acceptable loss.

 

[mgtfp]

You also have to consider that by increasing FC to 30ppm FC you are also increasing pH to likely above 8.0. The higher the pH, the higher the proportion of OCl^- as part of FC, which has a much shorter half-life in UV than HOCl. And at higher FC/CYA ratios this effect gets very significant.

That means that at SLAM-FC - and even more so at Mustard-SLAM-FC - you will have a much higher percentage of FC lost to UV compared to target-FC at normal pH.

Have a look at the explanation and the examples in this post:

Chlorine and pH relationships. Chem experts knowledge?

OK, so I am a newbie. But, I’m ignorant of pH within Chlorine relationships. I can find very much data here on Chlorine/CYA, but what about pH? Basically without getting too technical……haha, (I’ve read Chem Geeks articles) I am trying to figure out the effectiveness of Chlorine at different pH...

www.troublefreepool.com

I think your 12.5ppm loss at Mustard level are to be expected. That's why frequent testing and dosing during the daylight hours of a Mustard-SLAM are absolutely essential.

 

[DT770]

You also have to consider that by increasing FC to 30ppm FC you are also increasing pH to likely above 8.0. The higher the pH, the higher the proportion of OCl^- as part of FC, which has a much shorter half-life in UV than HOCl. And at higher FC/CYA ratios this effect gets very significant.

Can you please elaborate on the increase in pH? I'm not familiar with the OCL/HOCL relationship but current practice suggests that NaOH is balanced out by HCL.
FC was 11 ppm today at 11 am (A 1.5 ppm FC loss over a period of 16 hours). After diluting it 1:1 with distilled water, pH was measured somewhere between 7.5-7.8

 

[mgtfp]

When we say that bleach is pH-neutral, we mean that the whole chlorination cycle is pH-neutral. Adding liquid chlorine raises pH. Once FC is back down, pH is where it started).

During normal operation around target-FC, these pH-fluctuations are small and can be ignored. But while maintaining SLAM or even Mustard FC, pH will be elevated, which is why it's important to lower pH at the beginning of the SLAM.

While maintaining Mustard-FC, pH will be higher than during the regular SLAM part.

Here are some examples from chem geek about pH after adding larger quantities of bleach:

Use MA to neutralize pH effects of bleach?

When you guys add bleach, do you also add some muriatic acid to neutralize the pH effects? From other sites i've read, 1 gal of sodium hypo is pH neutralized with 5 fl.oz. of MA. If i'm gonna shock and initially bring the pH down to about 7.2 for higher sanitation strength, adding several...

www.troublefreepool.com

I ran a few calculations with Chem Geek's spreadsheet assuming TA 70 and CYA 50:

You start for example with with FC 6, pH 7.6, TA 70.
Then add MA to get to FC 6, pH 7.2, TA 64 (a test would show that probably still as 70, but for the further calculations I use 64).
Then add bleach to SLAM at FC 20, pH 7.9, TA 74 (had you not lowered pH first, it would already be above 8 at this step).
Then add more bleach to get to Mustard-SLAM at FC 30, pH 8.55, TA 81.

Once that FC has burnt off you will be back down to FC 6, pH 7.23, TA 64.

Mustard SLAMs are tough and need some chlorine to maintain FC for 24 hours.

Edit:
As you can see from the tables in the second half of Chem Geek's post that I linked earlier, FC burn-off due to UV will be higher at higher pH due to more FC being in the form of OCl^-, which has a shorter half life under UV than HOCl.