Any downside to SLAM?

jark87

Silver Supporter
Jun 5, 2011
214
Flower Mound, TX
I’ve had an on-going minor cloudiness issue for the past several weeks. My water chemistry has been great all summer and I had a filter issue that led me to believe that the cloudiness was a DE leak. I’ve replaced the filter grids and the air relief assembly, but the cloudiness remains. I raised my FC level to 6 several days ago just to see if it would change anything and the water did appear to clear up some. The water has had more debris recently due to rains, leaves falling and cedar elm seed production, so it’s time to get the cover on, but I’m planning to SLAM just in case I have an algae problem. My current test results are:

FC 4.5
pH 7.6
TA 70
CYA 70
CH 300
Salt 3200

Last night, FC was 5, so OCLT yielded a .5 drop. There was no FC loss in a test just a couple of weeks ago. I suppose the current FC loss could be due to the debris, even though I’m removing it pretty often.

So given that my only indication of a problem is slightly cloudy water, is there any risk in doing a SLAM? Assuming risk is low, how long does it usually take to get FC levels back down to normal once water is clear? I want to make sure everything is ok before putting the cover on. Last question: can the large amounts of bleach required to get to SLAM level be added all at once (understanding that it needs to be added slowly)?

Thank you!
 

Newdude

Well-known member
Jun 16, 2019
4,441
NY
My water chemistry has been great all summer and I had a filter issue that led me to believe that the cloudiness was a DE leak. I’ve replaced the filter grids and the air relief assembly, but the cloudiness remains.
98% of what people think are filter problems turn out to be chemistry problems the whole time. If the trouble persisted its probably the case here too.
The water has had more debris recently due to rains, leaves falling and cedar elm seed production
I have gone cloudy this time of year a few times when the late season dropping and farm dust was worse than usual. It’s entirely possible, and your .5 loss in the OCLT backs that up.
is there any risk in doing a SLAM
None whatsoever and if you didn’t need to do it the testing during will tell you so and it will be over real quick. If your hunch was right and you caught the algae bloom in time, it will be a much quicker SLAM than if you wait and have to play catch up.
how long does it usually take to get FC levels back down to normal once water is clear
The standard 2-4 ppm per day loss is always in effect. It’s probably on the lower end this time of year with the UV levels down from the peak demand of the season. It could take a week or more at 2 ppm loss per day, but no harm done in the meantime.
can the large amounts of bleach required to get to SLAM level be added all at once (understanding that it needs to be added slowly)?
Yes all at once per pool math. Bleach is always added as a quick correction. If anything, as long as your testing is good, the bleach degraded a little and you will undershoot the target. Calcium, CYA and salt have to be gradually raised because the only way to remove them is by draining. Chlorine will burn itself off quickly if you happen to overshoot a little. Dump away !!
 
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jark87

Silver Supporter
Jun 5, 2011
214
Flower Mound, TX
Well, algae is confirmed. While pouring in bleach I happened to spot a patch of the green stuff on the wall. After adding the bleach, I scrubbed the walls as well as I have in years 🙂. I’m a little perplexed about how it happened, as I’ve been more diligent about testing this year than any other year (not much else to do.) I’ve kept FC at 5 most of the summer, and it never dropped below 4. CYA has been at 70 since early summer. pH has always drifted, but has been kept in check, rarely exceeding 7.8. TA has been 70-80 all summer. First algae outbreak in many years! Gremlins.

Thanks again for the advice and support. I guess it’s about time I made a contribution. I’ve definitely gotten my money’s worth!
 

Newdude

Well-known member
Jun 16, 2019
4,441
NY
What is your runtime for the pump ? How many hours and when ? If there are sunny hours that the SWG is off it could easily eat 2 PPM and the same goes for bather load. The FC range is lower per CYA than the liquid chlorine chart because the SWG adds throughout the day little amounts at a time and the liquid users have to make it a full 24+ hours until the next dose. But a 2ppm window for you is cutting it super thin (even more so in TX)and doesn’t factor a weather event, incredibly hot day or busy swim day. Alot if us like to use the Liquid chlorine range for our SWG for the insurance. We like to 'run hot' and once you raise the FC level to the higher range, the SWG still adds its set amount for the day. It doesn't care if its raising you from 3-6 or 8-11. 3ppm is 3ppm. It only costs you a gallon and a half of liquid to bump up to 8ppm to start.
 
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Wobblerlorri

Bronze Supporter
I run at the top end of my chlorine range, which is 8 ppm, and never let it drop below 6 ppm. While I have had to SLAM three times this season, they've all been relatively short SLAMs because I caught the bloom early.

I would suggest keeping your chlorine at the upper end of your range instead of constantly flirting with the low end.
 
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jark87

Silver Supporter
Jun 5, 2011
214
Flower Mound, TX
I like to keep the water on the cooler side, so when I was running the chiller, I was running 17 hours per day with the SWCG at 25-30%. I’ve been running the pump 15 hours per day for the past couple of weeks with the SWCG at 35%. You both mention that I’m at the bottom end of the FC range, but according to the chlorine/CYA chart, my FC range is 3-5. Since I maintain at 5, isn’t that the high end? I’ve been managing at this level for years with no algae issues, but can easily adjust up if that’s what I should be doing. I’m just curious as to the discrepancy with the chart and what I’m not reading correctly.

The one thing I quit doing this year was using a phosphate remover. I’ll be going back to that once my SLAM is over, but I’ll be using one of the products recommend on this site rather than the Leslies product.
 

Newdude

Well-known member
Jun 16, 2019
4,441
NY
I’ve been running the pump 15 hours per day for the past couple of weeks with the SWCG at 35%
So thats plenty of runtime if its all during daylight. If you have 9 hours of sunshine and only 2 FC to buffer while the pump is off during the day it is a problem waiting to happen. This year was particularly hot too. There were a few folks in TX and FL that went to 90 CYA and many more that went to 80.

Since I maintain at 5, isn’t that the high
No it is the 'target'. You want to overshoot and fall down to the target and still have 2 ppm to spare between the target and your absolute minimum, never want to touch it, 3ppm. This was why I suggested using the liquid chlorine side of the chart. It will give you plenty of room to spare and won't hurt a thing. With a 70 CYA that is 8-10 per the FC/CYA Chart. It will take less than a gallon (but most of a gallon of bleach) to raise you from 5ppm to 9ppm and then the SWG will just maintain *THAT* like its been doing at 5ppm.
 
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jark87

Silver Supporter
Jun 5, 2011
214
Flower Mound, TX
Hmmm. Interesting. If the non-SWCG part of the chart is to apply to all pools, what’s the point of having 2 charts? I completely understand the logic of shooting high as a buffer, but I have my SWCG dialed in pretty well. I’d say 95% of my FC tests hit right on 5, which is the bullseye, not above or below. Because of this, I’m not experiencing the 2ppm drop that you are suggesting. It doesn’t appear from your signature (Wobblerlori either) that you are using a SWCG, so I understand that could be why you are making the suggestions. I’ve had great success with my parameters, as this is only my 2nd algae bloom in 13 years. I only noticed because the water is normally sparkling clear and recently was just slightly cloudy. And while we actually had a mild summer this year by Texas standards, I’d never take my CYA to 90. That level is not even listed on the SWCG chart and all of the official TFP information that I’ve read strongly advise against that, as it risks chlorine lock.

Thanks for the help with the SLAM!
 
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Newdude

Well-known member
Jun 16, 2019
4,441
NY
but I have my SWCG dialed in pretty well. I’d say 95% of my FC tests hit right on 5, which is the bullseye, not above or below. Because of this, I’m not experiencing the 2ppm drop that you are suggesting
Your 10ml test provides a one time snapshot of that sample out of 25k gallons of water. 12 hours later or 12 ft away could have a different result but be ok again at your spot by the time you test again. It doesn’t guarantee anything other than that spot at that time. YMMV of course. :)
It doesn’t appear from your signature (Wobblerlori either) that you are using a SWCG, so I understand that could be why you are making the suggestions
I have 8 years with my IC60. But it was just a suggestion to give yourself some wiggle room. Many members ride the dangerous line with good results. But nothing says you have to dance that close when raising the start FC will only cost you a $4 gallon of bleach. The SWG will maintain that higher level from there on out.
That level is not even listed on the SWCG chart and all of the official TFP information that I’ve read strongly advise against that, as it risks chlorine lock.
Chlorine lock is not a thing here. That’s the pool store talking. A couple members (literally 3?) had problems in the peak demand part of the season this year in hot climates similar to yours. As a last resort they went to 90 CYA and raised the FC accordingly. The guidelines are exactly that, Guidelines. You need to adapt what you’ve learned to fit your pools needs. We all wish you well and will help as we can to find that balance. Cheers !!