Drain first or SLAM

[pgjohnson]

Taken off the lights and cleaned inside, nothing much found, looked very clean, not any algae i can see, gave them each a good wipe out and vacuum.
So the pool has always been clear (for ever basically - did AA treatment in June) but FC dropped to 0 due to faulty chlorinator (possibly). Initially found some algae on top step tiles and then a day or so back in the drain.
Did get a lot of blown in debris which was around the time the FC was low but pool stayed clear.

First time I got 0.5 for OCLT - chlorine actually dropped between 0.5 and 1 after sun had gone from like 7pm (added chlorine) to 9pm
Next time I got 2 for OCLT - chlorine also dropped between 0.5 and 1 after sun had gone from like 7pm (added chlorine) to 9pm
So guess definitely something eating it, just surprised got a successful test but guess could be test error.

When I add chlorine, is it ok to just toss it into pool?

Pictures of pool attached.

 

[PoolStored]

When I add chlorine, is it ok to just toss it into pool?

Pour it in a pencil stream in front of a return and brush it around after pouring. Should be like a gallon every two minutes pencil stream.

Did you check the weir door for algae?

For OCLT, make your FC addition, pump running. Wait at least 30 minutes with pump running. Test after sunset. Leave your pump run, or allow 30 minutes of pump runtime in the morning and test FC before sunrise.

 

[pgjohnson]

So have just been tossing chlorine in and not brushing after, will do this better. Only throwing in less than .5 gallon each time generally.

Did check weir door (this is the skimmer box door?), cant get off but will try again

So doing my OCLT, I added last chlorine after sun gone (sun gone around 6pm, added around 7pm) then tested around 9pm.
Sun rise: 4:53 according to google but seemed light around 4:15/4:30am
Was not able to leave pump running in night so started pump around 5am one morning and was overcast and got a successful OCLT at 5:43am.
Next morning (today), started pump around 4:30am and tested at 5:00am and failed OCLT of 2ppm.

Pump is running on high speed when I add chlorine. If I don attempt to bother neighbors overnight I would need to at least run on low speed as its old and starting to become noisy.

Interestingly both nights after sun down and added chlorine at 7pm and tested at 9pm seemed to lose almost 1ppm, even first night when it only lost 0.5 from 9pm till next morning
eg 7pm Test chlorine 15ppm - added 0.5 litres --> tested 9pm was 15.5 ppm - after adding 0.5L should have gone slightly over 16
But if I my CYA is closer to 30 than 40 then maybe the excess over slam level disappears a bit even in darkness or is this not possible?

 

[pgjohnson]

Not sure I have the patience to keep going. Another failed OCLT test of 1.5ppm.
Pump was left running all night on low, first test 2ppm drop, then used pool brush to stir some water and got the 1.5ppm drop.
Chlorine actually held from 4pm (sun down around 6pm and shade on pool before 4pm) till 8:30pm last night so was hopeful.

Not sure what else I can do, can't find any spots where algae could be. Pool has always been clear and now got worse with iron staining starting to slowly show. Been adding chlorine every 2 to 3 hours 6 days now.

Any advice, desperate here.

 

[Texas Splash]

Paul, I have some questions/comments:

one morning and was overcast and got a successful OCLT

Once you passed, why did you continue to do more OCLTs? General rule is once you pass, you're done.

failed OCLT of 2ppm.

That was on Tues. That's a large drop for just overnight in what appears to be such a clean pool based on those pics. Sometimes looks can be deceiving, but I'm starting to wonder if there's not a different issue. I'll come back to that.

I would need to at least run on low speed as its old

Low speed is always fine.

But if I my CYA is closer to 30 than 40 then maybe the excess over slam level disappears a bit even in darkness or is this not possible?

I doubt it. It might effect the FC during the day, but there's not such a huge difference to where it should impact nightly testing.

Interestingly both nights after sun down and added chlorine at 7pm and tested at 9pm seemed to lose almost 1ppm, even first night when it only lost 0.5 from 9pm till next morning
eg 7pm Test chlorine 15ppm - added 0.5 litres --> tested 9pm was 15.5 ppm - after adding 0.5L should have gone slightly over 16

There should be no way you are losing 1 ppm of FC in just an hour or two right after the sun goes down. This makes me thing there is even a tester/chemical issue, or perhaps your testing method itself is somehow causing erratic results.

Also, you are never using that cover correct? At lest not now during the SLAM?

 

[Texas Splash]

I'm going to ask some basic questions since your thread is getting longer. You may have said it and I have missed it:
- Are you taking the water sample from the same place in the pool? Same depth (elbow deep), etc?
- Are you using the 10 ml water sample size for your FC testing? If so, it should be something like this:
**** 10 ml water sample with one generous scoop of powder (turns pink). Mix and add drops until the solution goes clear. Divide result in half. So 24 drops to clear would be an FC of 12.
- Are you using the speed/smart stir device?

 

[pgjohnson]

1. Yes same depth, elbow
2. Yes 10ml and dividing by 2.
3. No, just giving it a good shake before then continuously swirling with one hand while adding drops with the other.

Cover off for over a week or two now.

Last night I tested 4 times. Ist time 28 (14), 2nd time 33 (16.5), 3rd time 34 (17) and 4th time 33 (16.5) so took 33.

This morning first reading was 28 then 30 after quick swirl (30 seconds) near area with pool brush.

??? My pool does not seem to have many places where algae can hide. Have even gone around and scrubs waterline tiles. When we say looking for algae could we be talking an amount say as small as a fingernail?

Passed once and wanted to make sure so tested next night and failed by 2ppm.

I should add 375ml of chlorine to raise 1ppm. I have tested this in the past and its been accurate so from then on I generally test before then add and only retest at next addition.
At one stage yesterday (extremely hot 24 degrees Celsius) this happened:
- measured at 12:45pm - 24 (12) so added 1.75L
- measured at 1:35pm - 28 (14) so added 2L
- measured at 2:25pm - 30 (15) so added 1L
- measured at 4pm - 16.5 added nothing - shade over pool
- measured at 6:10 - 30 (15) added 0.5L - sun down
- measured at 8:30pm - 33 (16.5)

- measured next morning at 4:20am 30 (15) with pump running low all night.

So was hopeful the hold from 6:10 to 8:30 was going to give me a good OCLT.
CC still measuring at 0.

 

[Texas Splash]

- Remember, if your CYA is 30, the FC level would be 12. If your CYA is closer to 40, the FC should be 16. You seem to be hoovering about 2X that amount, so yes, that could explain erratic FC testing behavior. So if I'm understanding your FC numbers correctly (28, 30+, etc), let the FC fall down to about 12-14 (if your CYA is indeed around 30-40), then see how the FC tests go. It should be much more reliable.

- Pro tip: Get yourself a magnetic speed/smart stir. It makes testing sooooooo much easier and efficient.

 

[pgjohnson]

Thanks. No the 28/30 is the drops, FC in brackets.

I was wondering with the higher chlorine. Before you replied I though I might try 20ppm in case my CYA is greater than 40.

So lets say my CYA is 30 exactly and my SLAM should be 12. If I have it up near 16, is that possible to drop during night just because it is too high?

 

[Texas Splash]

If I have it up near 16, is that possible to drop during night just because it is too high?

It might drop a little, but not so erratically like having an FC at about 30. When the FC is 2X higher than it should be, testing becomes a bit unstable. Not nearly enough CYA in the water for the FC to bond to, so numbers get whacky. But I bet if you let it drop down to about 16 or so, it should settle down and be more reliable.

 

[pgjohnson]

Sorry for the confusion, FC around 15/16.

 

[pgjohnson]

Some things I wanted to understand if anyone has patience and could explain:

1. Can algae the of very small size, like a fingernail cause this or is that too small.
2. Lets say CYA is 30. So normal operation SWG would be 3-6, SLAM at 12.

• Now would it make any difference to OCLT is chlorine is at 12 or 4 for accuracy overnight?
• During the day would chlorine hold longer at 4 than at 12? So 12 would decrease quick the slower when closer to range of 3-6?

Thank you for all the help so far.

 

[Texas Splash]

Some things I wanted to understand

- Algae of any size is a potential problem Naturally the larger the growth the faster FC will fall. Problem with live algae is that is continues to grow if not physically disturbed (biofilm) so that chlorine can penetrate it. That's why hidden areas like in a ladder, hollow steps, or even under a drain cover can be a problem.

- An OCLT can be performed at many FC levels as long as that FC level isn't too high for the current CYA. So if the CYA is 30, an FC of anywhere between 5-12 is reliable for an OCLT. The problem with doing an OCLT too low is that if someone does have algae, the FC will fall even lower - below the recommended minimum FC level. But the OCLT is one tool to help diagnosis a potential problem.

- During the day, FC drop should be consistent if matched to the appropriate CYA. For example, if the CYA is 30, and the ideal FC range say 5-7 ppm (11.5% ratio), the FC should not fall more than 2-4 ppm in 24 hrs. If the FC is closer to the SLAM level of 12, there is less cyanuric acid for the free chlorine to bond to (ratio of about 40%), so some free chlorine could dissipate quicker. But during a SLAM, the elevated FC-to-CYA ratio is important to account for excessive organics and still battle the sun.

Since you replied to confirm your FC has actually been closer to about 16 and not 30, then there should not be an issue with FC dissipating too quickly unless there is algae still hidden somewhere. I agree that in your pool set up, it's quite simple with no hiding places except for under the drain. That may not be the issue, just saying I think that's the only place not actually confirmed.

The only other potential issues could be quality of the reagents or the testing itself, more specifically the mixing by hand. Many people do it, but it can be challenging to hold & stir with one hand while adding drops with the other. One or two droplets in error is all it takes to throw your test count off.

 

[Newdude]

Can algae the of very small size, like a fingernail cause this or is that too small.

Alage is microscopic and can only be seen once it's out of control. The whole pool may have algae that simply isn't at the level which is visible yet.

Lets say CYA is 30. So normal operation SWG would be 3-6, SLAM at 12

Slam is 40% of your CYA level.

Any operation level, for any type pool, is to be free and clear of minimum FC per their CYA level, at the low FC point in the day. SWG pools still swing daily, just not quite as much as liquid chlorine pools.

The FC target changes with daily demand at that point in the season. 3 FC may last days in the early/late season, and only 3 hours mid season.

Minimum FC
+ recent daily loss
+ 1 or 2 insurance FC
-------------------------------
= trouble free pool.

Now would it make any difference to OCLT is chlorine is at 12 or 4 for accuracy overnight?

No. But there is human error with you needing to make 24 perfect drops instead of 8.

During the day would chlorine hold longer at 4 than at 12? So 12 would decrease quick the slower when closer to range of 3-6?

Yes. Slam 'wastes' FC to the sun. It's burns off as a %, which is faster at higher levels. It's particularly felt by those slamming with higher CYA.

Clean your test vial well. (With alcohol if you have it) Many have failed an OCLT with a dirty vial. Or, the pool gods smiled upon them after cleaning it after failing several OCLTS. Lol.

 

[pgjohnson]

Wow thanks so much.

So my OCLT could be failing due to CYA at 30 and trying to test around 16.
Great so falls around 2ppm even 2 hours for a CYA of 30 with FC around 20 is ok.

Have cleaned out my drain thoroughly.

Currently trying to keep around 20ppm today, dropping 2ppm in 2 hours so far, overcast day. Still think CYA around 30 so after tonight will lower to around 12 for the next day and try from there.

 

[Newdude]

So my OCLT could be failing due to CYA at 30 and trying to test around 16.

No, the extra FC loss is during the day.

A dirty vial (even if it looks clean), or tester error (varying sample size or drops) may help you fail.

Or you still have algae.

after tonight will lower to around 12 for the next day and try from there.

Hang in there. You're near the finish line any way you slice it.

 

[pgjohnson]

Thanks for the support, just does not look like I am progressing with 1.5/2 drop every night.

Have tried to clean testing tubes.

 

[pgjohnson]

Just done a 2 tests in a row same vial.
Test 1: 29 so 14.5 FC
Test 2: 34 so 17 FC
Was watching the drops carefully so slowly so shouldn't be that far out.

This after a test 2.5 hours ago being 18 FC and adding 1.5L so should have hit over 20.

Think will let drop to 12ppm and test from there.

 

[pgjohnson]

Cleaned out lights again and return pipes and drain, nothing found.
Have left and will leave lights floating, have cleaned in light cavity well but nothing there. Although can't see algae growing there with no sunlight?
Saw specs of whatever inside light cover but cant open that and not sure if its just scratches etc. Also seems well sealed, see pics.

 

[pgjohnson]

Sorry for so many questions

1. From the FAS test page, why would this not be a factor when doing 30 drops and FC around 15? Could be out by 3 drops which is the 1.5ppm I sometimes get

• The precision of the measurement is plus or minus one drop when up to 10 drops of titrant are used, or plus or minus 10% of the final reading, when more than 10 drops of titrant are used.

2. Lets say you think CYA is 30 but its actually 40. Would running a SLAM at 12 instead of 16 work but just take longer?

Next Steps

• Chlorine dropped about 1ppm in the last 2 hours to 15ppm at 4pm.
• Going to let it drop (probably not much) till sun goes down around 6pm then test around 8pm.
• Tomorrow will keep around 12 as think my CYA is closer to 30 than 40