Advice needed on ending SLAM and when to resume SWG

3115581

Member
Nov 10, 2020
12
Newcastle, Australia
Hi All,

New Pool owner in Australia, about 4 months old (37000L, fibreglass, SWG). I've suspected a faulty SWG for a while as I haven't been able to get FC consistently over 1ppm pretty much since handover, but wanted to make sure my chemistry was sweet before going back to pool company.
Found out from a pool shop test that I had <10 CYA after about 6 weeks (handover guys only put in about 500g from what was left in the bag, and so added 1.2kg CYA and then some shock. 4 weeks later, no CYA again, and pool shop guy was stumped.
Since then, very little to no FC in pool, although it has been crystal clear with regular brushing and vacuuming (apart from the recent storms).

Decided to take matters into my own hands, and have been doing LOTS of reading over this site......

OCLT last night showed a drop from 9.5ppm to 6 (after manually dosing to get to 9.5), so started SLAM this morning. CYA is at 70, SLAM FC should be 28. Have been brushing and testing every 1.5 to two hours since 6am and adding relevant amounts of liquid chlorine to bring up to 28 (as per PoolMath app). On average, was losing around 3-4ppm between tests with <0.5 or 0 CC on every test. I have assumed that losses at higher FC's are proportional to some degree, and with extreme UV today, losses would compound - correct my assumptions if necessary.

At 6pm today (still very light - daylight savings) I vacuumed and changed cartridge, then tested and added chlorine to 28ppm. At 8.30, FC was still at 27 - I am aware tests are not overly accurate at these levels, but added another small dose anyway.

Plan from here is to leave everything as is overnight, retest in the morning, and if I haven't got a huge loss (less than 2 or 3 say - is this Ok at these levels?), let the day take its course. I figure that with a lower FC level tomorrow evening, I can get a more accurate picture of what an OCLT shows tomorrow night. As mentioned, water is absolutely crystal clear.

Does the plan seem sound at this point???

All going well, and I pass OCLT, when do I switch the SWG back on? At a certain FC???

Sorry, long post. I think I am well on track, just trying to sort out a few minor things. Appreciate any feedback.

And thanks for the site and forum - huge help!!!!!!!!

Cheers,

Mark
 

JJ_Tex

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The SLAM will take several days. You can do the OCLT in the morning, but keep in mind the 3 criteria to end a SLAM include an OCLT of less than 1.0:
Once you pass the 3 above, I would let your FC drift down to your target rate and then turn on your SWCG. You can also use pool math to calculate your FC output of your SWCG based on brand, run time, and % output.
 
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mgtfp

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Hey Mark, welcome to TFP!

I'd say 2-3ppm is too much for the OCLT, you should aim for 1ppm or less. Daytime UV-losses are more or less a percentage of your FC (at constant CYA), so higher FC means higher loss. But in the OCLT, in the absence of any UV, losses indicate that your FC is eating something. To a certain degree, that "something" can be CYA that your FC is destroying, especially at higher FC levels - that's why we say that up to 1ppm is acceptable.

If it's more than 1ppm, then it's highly likely that there are some organics in the water. Those organics will be destroyed by chlorine, maybe faster at higher FC, but any significant loss means that there is something in the water.

Only at FCs significantly above SLAM an OCLT above 1ppm might be acceptable (more CYA munching happening), and another OCLT at lower FC should be done.

Regarding SWG: Since this is a SWG with a history (has it been fixed/replaced now?), and you probably don't know the exact FC production rates yet, I wouldn't let FC come all the way down to your target before turning the SWG on, but start it a bit earlier. That gives you some buffer to verify that it is really working now and producing the chlorine amounts you are expecting. Since you can safely swim up to SLAM level (as long as you can see the bottom of the pool), that shouldn't add any delays to using the pool. Once you verified that the SWG is working as expected, let FC drift down to your target.
 

3115581

Member
Nov 10, 2020
12
Newcastle, Australia
Thanks All.

Given that I already psss two of the three SLAM tests, I guess my question is more about how I know when to try a proper OCLT.

From what I understand, at FC 28, the OCLT loss of 1ppm is less than the error margin of the test kit itself, and certainly less than user (ME) error. Thats where I thought maybe the 2-3 ppm loss would be acceptable to at least indicate a proper OCLT would be in order.

I tested this morning, and had a loss of only 2ppm, from 28 to 26. I dosed again anyway, seeing as I was working for the day. Tonight, at 6pm, FC was at 20, a little more manageable as far as testing goes. 6ppm daytim loss at this level would seem to be acceptable from what I read.

At 9pm, just a few minutes ago, I was still at 20ppm, so am leaving everything for the OCLT. Will let you know how it goes.

As for the SWG, I wanted to get chemistry correct before going back to company. That said, I've been crunching the numbers, and am happy to be corrected if assumptions are wrong....but I think my SWG just couldn't keep up.

With an initial OCLT loss of 3.5ppm over 8 hrs, assuming at least a consistent loss over time (f not more during daylight - does algae eat more FC during the day?) the other 16hours takes me to 10.5ppm minimum. Add another 2-4ppm for UV loss and we are approaching 15ppm loss in 24hrs.

My SWG puts out 23grams/hr at 100%, which in a 37KL pool is about 0.6ppm per hour (assuming the output rating is equivalent to 100% chlorine), or around 14-15ppm per day. At this rate, my SWG would struggle to replace losses even running 24/7! I've used PoolMath app to check some numbers using SWG, and it seems to align with my calcs - tell me if I am off here.

Anyway, running an OCLT tonight. If I pass, will let the FC drift down to around 8 before switching on SWG. This should give me a day or two to work out daytime losses, and adjust output/pump run time as needed.

Will post results tomorrow.

Cheers, and sorry for another long post!!
 

mgtfp

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Just looked at today's UV load in Newcastle, I think your daytime loss of about 6ppm (or 23% of your FC) sounds plausible. Certainly worth now to get up early in the morning to run a proper OCLT.

And yes, I could imagine that chlorine is more effective during the day in killing algae. These organics are usually more vulnerable while they're active, faster metabolism, easier for chlorine to get into cells and create havoc.

Regarding UV-losses, I usually experience around 20% loss during a sunny, high UV day (my CYA is 80ppm), on a cloudy day it's more like 10%. UV in Newcastle is a bit higher than here in Melbourne and your CYA is a bit lower, so I reckon around 25% loss is plausible. At the target FC for your CYA that should be very manageable with your SWG, once there's no more algae eating your chlorine.
 
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3115581

Member
Nov 10, 2020
12
Newcastle, Australia
5.30am this morning at FC 20, so 0 overnight loss (barring testing error).
At 6pm this afternoon, FC at 14ppm.
More of a loss than i would have liked, but with a UV index at Extreme, 11.5, for most of the day and some big winds I scooped out nearly a full net of leaves and vacuumed up a LOT of fine dust.
We are in a relatively new subdivision, so everyone's yards (including ours) are pretty much still dust (very fine clay dust, almost like chalk/talc). I think this will be my nemesis for some time- that and our gum trees, which drop leaves year round, but I absolutely will not cut down. Overall, taking a 6ppm loss from 20ppm with a grain of salt at this stage.

Will do another OCLT tonight once dark and see how it goes.

Cheers,

Mark
 

mgtfp

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Looking not too bad. 6ppm loss during the day from 20ppm is probably still on the high side of normal, and you passed the OCLT. I think you already mentioned that you passed the other criteria? Water is clear and no significant CC? See how the OCLT goes next night. And to be sure, you could keep FC for a while a bit higher, like the high end of the non-SWG target range. That gives you some buffer to not dip too low in case there is still something lurking in the water.

If you want to get an idea how your UV-index varies during the day, there is a great page from the Aussie Government:
 
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poolnoobgrandma

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I think almost every SWG owner has thought the system wasn't working at one time or another, only to find that something else was going on, and that after a SLAM the SWG could keep up just fine. If I were you, I'd turn on the SWG when the chlorine is around 11 or 12, so you have some wiggle room to adjust.
Get the SWG dialed in to the point that the FC level is still going down very slowly, then, as you get closer to your target, dial it up (either run time or percentage) until you have landed on your target and stay there.
Remember, you can swim while this is going on. It's safe to swim up to the SLAM level for your CYA.

Good luck!
 

Mdragger88

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Looks like You’re on the right track- but be sure to remove & scrub light niches, skimmer throats, ladders etc. before u end SLAM Process to be absolutely certain u got everything. & do an Overnight Chlorine Loss Test @ slam level for your cya.
 

3115581

Member
Nov 10, 2020
12
Newcastle, Australia
Thanks again all.

FC loss overnight was <=0.5, so looks good.

We have a relatively overcast day here today, but still very high UV index, and possible rain forecast. Will be interesting to see losses so thought i might leave it for the day again. Currently at FC12.5 and am hoping to still have 9ish this afternoon. If lower I'll dose to 10 before turning on the swg tonight and measure output.

My cya is currently at 70 (thats my test kit, and aligns with the 68 measured at pool shop a couple weeks ago). If todays losses are higher than expected, I'll increase that to 80 over the weekend and keep measuring twice daily.

Haven't cleaned behind lights (bit hesitant to remove on a new(ish) pool), but found a bit of green in the top of the filter housing - wondering if air trapped here helps algae grow, since it won't be recieving as much chlorine exposure?

Will keep posted over the weekend.

Cheers.
 

mgtfp

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remove on a new(ish) pool), but found a bit of green in the top of the filter housing - wondering if air trapped here helps algae grow, since it won't be recieving as much chlorine exposure?

You have a cartridge filter, right? I don't have any experience with them. I used to see algae in that viewing glass of my sand filter that's been used during backwashing. After having this properly slammed out, I now flush that area from time to time with fresh pool water by pumping some water to waste for a few seconds.

If that green is within your normal water flow, then you should clean that out. Not sure how accessible that is, try to get there with a brush, a spray bottle with SLAM water, whatever.

That could explain why you have no issues passing the OCLT, when your pump is not running over night, but during the day you are pumping water past that spot, resulting in your daytime losses being still on the high side.
 

wireform

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Aug 15, 2017
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Thanks All.

Given that I already psss two of the three SLAM tests, I guess my question is more about how I know when to try a proper OCLT.

From what I understand, at FC 28, the OCLT loss of 1ppm is less than the error margin of the test kit itself, and certainly less than user (ME) error. Thats where I thought maybe the 2-3 ppm loss would be acceptable to at least indicate a proper OCLT would be in order.

I tested this morning, and had a loss of only 2ppm, from 28 to 26. I dosed again anyway, seeing as I was working for the day. Tonight, at 6pm, FC was at 20, a little more manageable as far as testing goes. 6ppm daytim loss at this level would seem to be acceptable from what I read.

At 9pm, just a few minutes ago, I was still at 20ppm, so am leaving everything for the OCLT. Will let you know how it goes.

As for the SWG, I wanted to get chemistry correct before going back to company. That said, I've been crunching
I think almost every SWG owner has thought the system wasn't working at one time or another, only to find that something else was going on, and that after a SLAM the SWG could keep up just fine. If I were you, I'd turn on the SWG when the chlorine is around 11 or 12, so you have some wiggle room to adjust.
Get the SWG dialed in to the point that the FC level is still going down very slowly, then, as you get closer to your target, dial it up (either run time or percentage) until you have landed on your target and stay there.
Remember, you can swim while this is going on. It's safe to swim up to the SLAM level for your CYA.

Good luck!
I would say the other way around with starting up the SWG. Start it high and dial it down to help the FC land where you want it to be since you're loosing a lot to the daily UV. Point number 2 would be now that the OCLT is done break open the filter and get those cartridges clean so that nothing lingers in there and turns your hard work around.
 
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3115581

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Nov 10, 2020
12
Newcastle, Australia
So yesterdays daytime losses were good. Down from 12.5 at 5.30am to 11 at 9pm.

However, looks like my swg is not working correctly. Rsn the pump and cell for exactly 8 hrs from 9.30 to 5.30am, at 100% output. This morning my FC was 12 at most, an increase of only 1ppm.

The swg is meant to put out 23grams/hr, so I would be expecting an increase of around 4-5ppm in my 37KL pool (around 0.6ppm per hour).

Will run another test tonight and then anothr OCLT om sunday. That way i will have 2 (failed) SWG tests bookended by successful OCLT's to take back to the pool company/manufacturer.

When looking at the cell, gas only seems to be coming off one plate - i asked the pool technician about this and he said it was normal. Is it? That plate is slightly whiter than the others. Will post a video if possible.
 

mgtfp

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That doesn't sound right.

If you want to post a video, you have to upload it first. In the menu, under "Media", you "add media", either in a predefined category, or create your own album - I think that should work, haven't done it myself so far...

Video would certainly help.
 

3115581

Member
Nov 10, 2020
12
Newcastle, Australia
Update;
Wednesday and Thursday nights i had zero chlorine loss with swg off.
Friday and Saturday nights, swg on for 8 hrs at 100% for a 1ppm increase max (actually measured 0.5).
Sunday night swg off, and another zero loss night. Last night had my first overnght loss of 1ppm with swg off, but we did get some rain and i scooped out half a net full of leaves.

FC levels have been driftng down slowly, at around 7ppm this morning. Just threw in a touch of acid, ph at 7.7-7.8 (I struggle differentiating the colours).

Waiting for a call back today from lead technician at pool company and will let you know how it goes.
 
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