SWG on or off during SLAM?

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SunnyOptimism

SunnyOptimism

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Jun 20, 2014
850
Tucson, AZ
Question - During a SLAM, should the SWG be on or off?

My OCLT was -3ppm (started at 5ppm). My water is crystal clear and I just went through a long partial drain and refill process to get my CYA under control. I'll have more test results soon but my numbers should all be within suggested ranges. I was going to start the SLAM tonight after sundown.


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The SWG should certainly be off when doing an OCLT. Otherwise, it can be on or off as you please, keeping in mind that it is not going to be able to be the primary chlorine source for a SLAM. But it can supplement your manual additions. Because of the OCLT interaction, it is often simplest to leave it off.
 
JasonLion said:
The SWG should certainly be off when doing an OCLT. Otherwise, it can be on or off as you please, keeping in mind that it is not going to be able to be the primary chlorine source for a SLAM. But it can supplement your manual additions. Because of the OCLT interaction, it is often simplest to leave it off.
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Thanks JasonLion.

My system (pumps and SWG) don't run over the night as per my current schedule (9am to 6pm). So my OCLT results are a true representation of the FC loss without sun and without SWG.

I just went to Ace and bought 12 gal of 10% chlorine bleach for $9.45 per 2 gallon bottles. That's $4.75 per gallon or about $0.48 per % bleach. Don't know if it's a good deal but I wanted to start my SLAM off strong!



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I will add that you want the pump to run at least 30 minutes after the last chemical addition (this includes from the SWG) before you test at night. Also, the OCLT was designed to be performed at/near shock level. Finally, IMO, it is best to have the pump running overnight for the OCLT so that the water stays mixed (you would certainly need the pump to run at least 30 minutes before you test in the morning and can not have the SWG on during that time either).

For all these reasons, it is typically easier to get a feel for how the process is going and not make a mistake by just having the SWG off for the entire SLAM.
 
Just to clarify my OCLT procedure -

1) measured FC at 2ppm after system shut off at 6pm
2) turned pumps and SWG back on and added enough 8.25% bleach to get up to 5ppm by PoolMath

3) waited 30 mins and confirmed 5ppm FC

4) shut system off entirely

5) measured 2ppm in the morning before any sunlight

FYI - all skimmer baskets, pump baskets and in line leaf traps were fully cleaned of any debris and I had just completed a full back washing with new DE addition to my filter. I also had recently added salt as well that day to compensate for the recent water replacements I was doing to lower CYA.

The pool water was mixing for about 6 hours prior to the OCLT but maybe there wasn't enough turnovers? Could the backwash plus new DE suck up FC? Any effect of back washing on FC levels?


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That is certainly a fail, and seems to be missing a few key points I made in my previous post ... run the pump for 30 minutes after any addition of FC (you SWG was likely generating until you turned off the pump) before you test in the evening. Run the pump at least 30 minutes before you test in the morning (no SWG).

Backwashing should have no effect on the FC levels.
 
jblizzle said:
That is certainly a fail, and seems to be missing a few key points I made in my previous post ... run the pump for 30 minutes after any addition of FC (you SWG was likely generating until you turned off the pump) before you test in the evening. Run the pump at least 30 minutes before you test in the morning (no SWG).

Backwashing should have no effect on the FC levels.
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Thanks!!

I will rerun the OCLT again tonight as well as post a full set of water test results that I'm planning to do today to confirm exactly where my CYA level.


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Ok. So here are the numbers at 2pm local time with high hot sun -

SWG running at 65%

FC 1.8
CC 0.2
pH 7.6
TA 110
CH 400
CYA 70
Salt 3800 (AquaChek strip)

I'm thinking I'm going to start a SLAM at sundown and see what my OCLT is based on the procedure that jbizzle suggested above.

Water is clear but I fear my IC40 is working too hard and there's nasty creatures lurking about.

Any thoughts or rebukes?


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You FC is certainly too low so you either need to up the pump on time and/or the SWG output or boost it with bleach and do the OCLT to see if something is in the water.

This heat is BRUTAL!!! Can't wait for the cooling of the monsoons (minus the humidity ;) )
 
jblizzle said:
You FC is certainly too low so you either need to up the pump on time and/or the SWG output or boost it with bleach and do the OCLT to see if something is in the water.

This heat is BRUTAL!!! Can't wait for the cooling of the monsoons (minus the humidity ;) )
Click to expand...

Alright. I want to ease my algae anxiety disorder (AAD) so I'm going to start the SLAM this evening and see what I get for OCLT. I certainly have some runway left with more pump on time and/or increased SWG output. I could also program in some high speed steps during the day (I typically run straight at 2500 RPM which is ~ 1kW power usage). A few high speed shots during the day would bump more H2O flow through the cell.

Agreed, heat is brutal but I love it. I grew up in NY with soupy nasty humidity in the summers so the little humidity bumps here during monsoon season are nothing to me. They actually feel good and I totally love watching the temp go from 105 to 75 in the span of 15mins when the rain kicks in!!! I will take 105 & dry over 95 & 95%RH any day!!



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I totally agree. The heat and dry is not really a problem ... except when I need to be outside in the sun working in the yard :shock: And the drastic temperature drops are pretty cool.

Something to check (that just bit me), make sure your SWG is generating on low speed. My pressure on high had only risen about 15-20% and was near time to backwash, but I discovered that my flow rate on low had dropped by 50% and the SWG was not actually working for at least a few days when on low and my FC dropped too low. It would generate on high in the morning when the solar was running, but then not in the afternoon while on low speed.

That said, with your bigger pump and higher running speed, that is not likely the problem.
 
jblizzle said:
I totally agree. The heat and dry is not really a problem ... except when I need to be outside in the sun working in the yard :shock: And the drastic temperature drops are pretty cool.

Something to check (that just bit me), make sure your SWG is generating on low speed. My pressure on high had only risen about 15-20% and was near time to backwash, but I discovered that my flow rate on low had dropped by 50% and the SWG was not actually working for at least a few days when on low and my FC dropped too low. It would generate on high in the morning when the solar was running, but then not in the afternoon while on low speed.

That said, with your bigger pump and higher running speed, that is not likely the problem.
Click to expand...

Good points. I'll keep that in mind

I'm usually pretty obsessive about checking the filter pressures and making sure I've got green lights on the IC40. Bonus with the EasyTouch system is my remote will feedback errors like no flow so I don't have to walk outside to the equipment pad. But I always feel the need to give the pressure gauge the old eyeball check at least once a day.

Your advice has been very helpful. I'll post up some results tomorrow morning. Hopefully I'll get this all squared away soon because my wife is about to kill me for spending so much time on the pool (no swimming until daddy makes the water perfect....it drives them nuts :) )


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Sketchy results to report. So for some reason my PoolMath was way off and I wound up adding enough 10% bleach to get my FC up to 52ppm!!! I was targeting 28ppm.

In the morning it was down to 32ppm (pumps on, no SWG). So I'm losing ~ 2ppm per hour overnight.

I'm starting to run low on reagents so I'm going to target adding 1qt per hour or so over the day (1qt should raise FC by 1.5) and then see where I am tonight. Reagents are on order but I likely won't get them prior to Friday.

Oi, so sad :(


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Abigail K said:
Did you check you entered the correct current and target values, correct pool size, correct measurement units and correct bleach strength?
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Yep. Everything was correct. I think my mistake was to add the full amount (slowly) instead of doing half and then measuring. I'm always very wary of doing large volume chem additions.

PoolMath has never failed me before so I'm thinking it was late at night and I just goofed a number somewhere.

I'm now down below mustard algae shock levels so I'll do small additions throughout the day and then figure out where I am tonight. Sadly, I've got maybe one or two more tests before I run out of Taylor reagents.

Any idea if Leslie's sells comparable reagents to Taylor? I really need the R0871 titrating reagent


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OK, things are looking up :party: Here are some more results -

Kept up the SLAM levels of FC yesterday doing regular additions of 1 QT of 10% liquid chlorine. Started the day at 31ppm (high, I know) and add about 7ppm of FC over the day. I also had the SWG running at 1/3 percentage which translates roughly into adding an additional 1.5ppm of FC over the full run time of the system (assuming you trust all the numbers related to what my IC40 can generate).

Ended the day at 34ppm FC and <0.2 CC.

OCLT - (about 10.5 hours overnight to next morning) -

FC 31ppm and CC ~ 0ppm

SO that's a loss of 3ppm overnight of about 0.29 ppm/hr. If you trust my numbers during the day, the total burn rate of FC was ~ 0.5 ppm/hr and the night before when I started the SLAM my overnight burn rate on FC was close to 2ppm/hr. So, burn rates in order are -

2ppm/hr
0.5ppm/hr
0.29ppm/hr

SO the burn rate is decreasing pretty rapidly and I'm going to continue to SLAM today to try to achieve the Holy Grail value of less than 1.0ppm FC loss overnight. I know my burn rate will go up during the day, but I hope to see a lower burn rate (0 would be nice) overnight into tomorrow.

Question for the experts - isn't expressing an OCLT as an absolute loss (1ppm or less) less accurate or less appropriate (pool volume a factor?) than looking at an FC loss rate? Isn't using an absolute amount of FC arbitrary? Just wondering where that criterion came from and what it is based on....
 
Talking about "burn rate/hr" is meaningless. Chlorine loss depends on the starting FC level, so the hourly rate will vary (because the FC level as the start of each hour is different). This is especially true when the FC loss is high, most of it will happen quickly near the beginning. When the FC loss is low, nearly all of the difference is going to have to do with testing repeatability problems, which has nothing to do with time at all.

Expressing an overnight loss as an absolute FC number is the only approach that makes any sense.

Also, the absolute number doesn't mean anything, only relative numbers are interesting. You loss last night was lower than your loss two night ago, so things are improving.
 
JasonLion,

Thanks.

I certainly understand an absolute number is probably just the easiest thing to measure and it's the trend that is important not so much an absolute number.

FC loss rate would probably only be useful if there was an accurate way to probe FC instantaneously over time like an ORP probe. Then you could easily see the trend in the data. But nothing reliable like that exists so it's really all just an academic discussion at this point.

I'll post more results tomorrow when I can do another OCLT. Hopefully my reagents will hold out :(


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I suppose, except that there is no value I can think of to seeing the trend even if you had the equipment to do so. The test needs to be over quite a few hours so the signal is large enough to "hear" over the noise, and it really is a yes/no test (algae/no-algae).
 

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