OCLT - does duration of the night matter?

[mgtfp]

Is that because we never reach the point of making the pool water sterile and hence there are germs/bacteria that are always being dealt with by the chlorine? Or would this be the case even if the pool was 100% bacteria/virus/germ free?

Not talking about organics here, just chlorine reacting with "stuff". For example CYA - that's for example how CYA slowly degrades, it's getting oxidises by chlorine. Or chlorine reacting with a plastic pool cover. Whatever.

 

[mgtfp]

Does the diluted test reduce the accuracy?

I should. Just getting the mixing ratio right adds another level of testing tolerances.

 

[novice123]

Not talking about organics here, just chlorine reacting with "stuff". For example CYA - that's for example how CYA slowly degrades, it's getting oxidises by chlorine. Or chlorine reacting with a plastic pool cover. Whatever.

But this increased rate of oxidation doesn’t affect the OCLT does it?

 

[mgtfp]

That's why the criterion for a successful OCLT is 1ppm and not 0ppm chlorine loss, to account for chlorine losses that are not due to algae consuming chlorine (having excluded losses to UV light by doing the test between sunset and sunrise), and to have some margin for testing errors.

The 1ppm is designed to cover possible non-algae induced losses at typical summer pool temperatures and chlorine levels up to about SLAM-FC over a typical summer night duration. Once you go too far beyond that (for example at Mustered SLAM FC level), an OCLT may become inconclusive and should be repeated.

Your situation should be in range, but you may have higher testing errors with the Photometer compared to a FAS/DPD titration. As I said, I would repeat the test at a level that doesn't require dilution.

 

[novice123]

That's why the criterion for a successful OCLT is 1ppm and not 0ppm chlorine loss, to account for chlorine losses that are not due to algae consuming chlorine (having excluded losses to UV light by doing the test between sunset and sunrise), and to have some margin for testing errors.

The 1ppm is designed to cover possible non-algae induced losses at typical summer pool temperatures and chlorine levels up to about SLAM-FC over a typical summer night duration. Once you go too far beyond that (for example at Mustered SLAM FC level), an OCLT may become inconclusive and should be repeated.

Your situation should be in range, but you may have higher testing errors with the Photometer compared to a FAS/DPD titration. As I said, I would repeat the test at a level that doesn't require dilution.

Thanks a lot for this

 

[novice123]

So came back and checked the pool and found this at the bottom. Is that dead algae? There was nothing like this yesterday as I vacuumed.

Should I continue the SLAM? Just getting pressured by the mrs and kids who are getting impatient.

I can’t see where the algae can come from other than the pool light fixture? Is it normal to have to remove that and wash inside it?

 

[mknauss]

Just getting pressured by the mrs and kids who are getting impatient.

To swim? Let them. As long as FC is at or below SLAM level based on your CYA, and you can see the bottom of the deep end of the pool, go swimming.

 

[novice123]

To swim? Let them. As long as FC is at or below SLAM level based on your CYA, and you can see the bottom of the deep end of the pool, go swimming.

Why does it say on poolmath after I enter a rounded figure of 40 cya that the slam target is 17 yet it says “your target is outside the recommended range!”
Then why is it suggesting this figure?

 

[Newdude]

your target is outside the recommended range!”

Slam isn't a normal range/value.

Once we get you fixed up, and teach you how to keep it that way, it will never come up again.

 

[novice123]

Ok I’m even more confused now. At sundown today the fc went down by 1.3 only to 10.4 from 11.7. The uv was off throughout. That's for the duration of17.5 hours with no pool cover. Yet yesterday from sunset to sunrise, 6h35m, it went down by 1.7. I had the pool uv on for about 3hrs during this time.

Does this mean
1. The organic stuff is finally coming down to zero?
2. Or is the uv system responsible for the extra chlorine loss?
3. It's due to the innacuracy of the poollab?

 

[PoolStored]

Does this mean
1. The organic stuff is finally coming down to zero?

Potentially, only OCLT will tell.

2. Or is the uv system responsible for the extra chlorine loss?

Yes. I would turn off and remove the UV system. That is what I did, not needed, uses electricity and consumes FC.

3. It's due to the innacuracy of the poollab?

Potentially...we'll never know.

 

[mgtfp]

Yes. I would turn off and remove the UV system. That is what I did, not needed, uses electricity and consumes FC.

This is an indoor pool, so UV could make sense in this case.

 

[PoolStored]

This is an indoor pool, so UV could make sense in this case.

Missed that! Good catch. Lots of threads this month...

 

[novice123]

24 hours later since the last test and fc went down by 1.2

Before the last test, Yesterday, I brushed and vacuumed a few hours before taking the test.

Today I found this again:



What is this?

 

[PoolStored]

Likely dead algae. Did you continue the SLAM? Did you do the OCLT?

 

[novice123]

Likely dead algae. Did you continue the SLAM? Did you do the OCLT?

I failed the test once then one of the knowledgeable ppl here advised I let it come down within the range that I can test without using distilled water.

Currently fc is at 9.2 and it is coming down really slowly so I’m thinking is it worth raising the level? Like what good would the extra fc do?

 

[PoolStored]

I failed the test once then one of the knowledgeable ppl here advised I let it come down within the range that I can test without using distilled water.

Right. You should do the OCLT with a range of FC that will work for your unit.

Currently fc is at 9.2 and it is coming down really slowly so I’m thinking is it worth raising the level? Like what good would the extra fc do?

Why raise it again if your are letting it come down to do OCLT.

I'm confused.

 

[novice123]

Why raise it again if your are letting it come down to do OCLT.

I'm confused.

Sorry I meant about the slam process, if I didn’t have the issue of lowering it for testing purposes, even then what would be the reason to raise the fc to slam level (which I’m assuming I would do due to the dead algae that I’m seeing everyday and hence failing the “clear water” part of the test) Like what purpose would the extra fc serve? I’m just trying to understand the process better

 

[PoolStored]

Shock level for TFP is 40% of the CYA value. That roughly gives a little over 1 to 1.5ppm hypochlorous acid (HOCl) concentration which is the primary disinfectant and oxidizer for chlorine. 1ppm HOCl is about 20X the concentration of HOCl at the standard target FC levels. This level over TIME will eradicate algae. If you are seeing dead algae, then there is still live algae, even if you can't see it.

There’s nothing magical or scientific about the 40% value. It’s simply a trade off between safety (of equipment and surfaces), rate of clearance, and efficient use of liquid chlorine, which is not cheap these days. Pool service companies have been known to shock pools at much higher levels (100% of CYA) to clear a pool fast but that is very dangerous and could easily bleach out a pool surface.