Should I SLAM?

[SloppyJosh]

I've been slowly getting our pool balanced.. This is the first time I've really taken it into my own hands and not used our local pool supplier. Last year it was cloudy and they couldn't help me get it sorted.

The pool is a 25' vinyl above ground, water depth is ~48 inches.. I have a K2005 test kit.. I have the FAS-DPD reagents on the way but they probably won't arrive for several days. PH is ~7.5, TA is 170 (going to fix this soon with acid/aeration),

The water is quite clear... CYA is sitting in the mid 30s, I just added a bit more CYA (~1lb) that should get me up to the low 40s. Trying to sneak up on getting my CYA where I want it so I don't get it too high.

I've been testing my FC in the morning and evening, then bringing it up to ~4ppm. It seems like it's taking a lot of chlorine to keep it maintained... Some days I've put a whole gallon in it (though that was before I had my CYA up to the 30s.. it was previously <20). Seems like I'm having to add ~5-6ppm/day.

Family was in yesterday and when they got out FC was ~1. A few hours after everyone was out and after sunset I brought FC up to 6. This morning, I retested and it was ~4. Now at 1 PM and FC is ~1.5. Nobody has been in the pool. Pool is in full sun for a few hours now.

So my questions are.. while I know that's not a proper OCLT... is what I'm seeing a strong enough signal that there's still something in the pool and I need to go ahead and SLAM? I'd rather not SLAM if I don't have to. Could that overnight loss be from sanitizing anything that was left in the pool from the family swimming? Could the loss during these couple hours of sunlight just be that my CYA is in the lower range? Is it that 5-6ppm is a normal amount of daily chlorine? I'd expect it to be closer to 3ppm/day.

 

[JimMarshall]

4-5 can be a normal daytime loss in high UV times. I would definitely plan on SLAMing once you get your FAS-DPD. Also, 4ppm should be the low end of your FC. I suspect that you are hovering on the verge of an algae bloom.

WHy do you say that you don't want to SLAM?

 

[bobloblaw42]

Without FAS/DPD test, your OTO TC (not FC) readings are just approximations

SLAM guidance suggest SLAM when you (1) can see algae, (2) have combined chlorine above 0.5, or (3) OCLT is greater than 1.0. You need the FAS/DPD test to reliably answer whether the 2nd or 3rd criteria apply to you.

Also, we recommend you round up your CYA readings. So if you approximate your CYA is 41 to 49, that would be a 50 for purposes of apply TFP guidance. Assuming you use liquid chlorine, at 50 CYA your target is 6-8FC which is higher than your OTO test can measure and higher than you have been previously adding (targeting 4ppm). As a result, you are likely teetering on the edge of an algae bloom but hasn't arrived because you are diligent in adding chlorine daily.

Until your FAS/DPD test comes in, would recommend adding chlorine until your OTO test is a much darker yellow than the 5ppm on the color comparator. This is about 3 quarts to a gallon a day of 10% LC. Once your test comes in, post the results. Consistently maintaining 8FC (top end of range) may clear up the marginal ability to hold chlorine and you might see usage fall back to your expectation of 3ppm / day.

You can always SLAM but that would require even more chlorine and you would want your FAS/DPD reagents anyway so you can check back in when you have test results before making that call.

 

[SloppyJosh]

4-5 can be a normal daytime loss in high UV times. I would definitely plan on SLAMing once you get your FAS-DPD. Also, 4ppm should be the low end of your FC. I suspect that you are hovering on the verge of an algae bloom.

WHy do you say that you don't want to SLAM?

I dunno, I suppose it just seems like a lot of chlorine for the kids to be in... And I've read that it's safe to be in with at at/below SLAM level but won't we notice the stronger chlorine in it? I guess I'm basing that on guidance as if I were putting pounds of shock in the pool and not supposed to re enter the pool until chlorine has went back down.

Without FAS/DPD test, your OTO TC (not FC) readings are just approximations

SLAM guidance suggest SLAM when you (1) can see algae, (2) have combined chlorine above 0.5, or (3) OCLT is greater than 1.0. You need the FAS/DPD test to reliably answer whether the 2nd or 3rd criteria apply to you.

Also, we recommend you round up your CYA readings. So if you approximate your CYA is 41 to 49, that would be a 50 for purposes of apply TFP guidance. Assuming you use liquid chlorine, at 50 CYA your target is 6-8FC which is higher than your OTO test can measure and higher than you have been previously adding (targeting 4ppm). As a result, you are likely teetering on the edge of an algae bloom but hasn't arrived because you are diligent in adding chlorine daily.

Until your FAS/DPD test comes in, would recommend adding chlorine until your OTO test is a much darker yellow than the 5ppm on the color comparator. This is about 3 quarts to a gallon a day of 10% LC. Once your test comes in, post the results. Consistently maintaining 8FC (top end of range) may clear up the marginal ability to hold chlorine and you might see usage fall back to your expectation of 3ppm / day.

You can always SLAM but that would require even more chlorine and you would want your FAS/DPD reagents anyway so you can check back in when you have test results before making that call.

I'm using the DPD test in the K2005 to test for FC, It goes up to 10ppm, I think.. so I'm good to pull it up to ~8ppm reliably. When I use that test for FC/TC/CC I can't really see much color difference between the FC and TC.. but I know that's not a very accurate measure.

Thanks for pointing out that my target FC is too low, I'd forgotten to go back and adjust my target level now that I've raised my CYA.

I think holding it around 8ppm is the way to go for the short term to see if that gets me back down to my ~3ppm/day then I'll reevaluate once my FAS/DPD reagents get here as suggested and could do the SLAM properly if needed.

Thanks!

 

[bobloblaw42]

Ah, the comparator of the 2005 does go up to 10. You'll like the precision of the drop test red to clear better anyway, when available.

 

[JimMarshall]

I dunno, I suppose it just seems like a lot of chlorine for the kids to be in... And I've read that it's safe to be in with at at/below SLAM level but won't we notice the stronger chlorine in it? I guess I'm basing that on guidance as if I were putting pounds of shock in the pool and not supposed to re enter the pool until chlorine has went back down.

It is perfectly safe to swim up to SLAM levels, and the difference cannot be noticed. The "Chlorine smell" that you'd experience in a non TFP pool is a result of high CC levels, and is not typical. The "chlorine sting" in the eyes is typically unbalanced pH. Due to the effect of CYA on FC, there is actually less sanitizing power at 16 FC and 40 CYA than you'd find in tap water with a FC of 1 and no CYA. TFP is all about understanding the chemistry and knowing exactly what we put in our pools and what the effect will be.

 

[SloppyJosh]

It is perfectly safe to swim up to SLAM levels, and the difference cannot be noticed. The "Chlorine smell" that you'd experience in a non TFP pool is a result of high CC levels, and is not typical. The "chlorine sting" in the eyes is typically unbalanced pH. Due to the effect of CYA on FC, there is actually less sanitizing power at 16 FC and 40 CYA than you'd find in tap water with a FC of 1 and no CYA. TFP is all about understanding the chemistry and knowing exactly what we put in our pools and what the effect will be.

Right on.. thanks for clearing that up for me.. the chlorine smell has been getting stronger lately.. which I thought was the result of me pushing the chlorine a bit higher.. which is why I was hesitant to really raise it so high.

In the mean time, am I good to go ahead and bring the TA down to within range? To double check my understanding.. I need to lower PH to 7.0-7.2 then aerate to raise the PH back up. With my TA being that high, will that require a few rounds of the acid/aeration to lower it? According to the pool math calculator I'll need 24oz of 31.45% muriatic acid to bring PH down to 7.0 and that'll only lower my TA by 6.7... At that rate I'll have to do it about a dozen times. Which.. is what it is.. but mostly I just want to make sure I buy enough acid.

 

[JimMarshall]

Right on.. thanks for clearing that up for me.. the chlorine smell has been getting stronger lately.. which I thought was the result of me pushing the chlorine a bit higher.. which is why I was hesitant to really raise it so high.

In the mean time, am I good to go ahead and bring the TA down to within range? To double check my understanding.. I need to lower PH to 7.0-7.2 then aerate to raise the PH back up. With my TA being that high, will that require a few rounds of the acid/aeration to lower it? According to the pool math calculator I'll need 24oz of 31.45% muriatic acid to bring PH down to 7.0 and that'll only lower my TA by 6.7... At that rate I'll have to do it about a dozen times. Which.. is what it is.. but mostly I just want to make sure I buy enough acid.

The fact that you're getting more "chlorine smell" is further evidence supporting my suspicion that your FC is being consumed oxidizing organics (algae) in the pool. You are safe to lower the TA, but it's not something that you NEED to "fix" or chase into some magical range. You can just keep dosing to lower pH and your TA will come down over time.

 

[Newdude]

I guess I'm basing that on guidance as if I were putting pounds of shock in the pool and not supposed to re enter the pool until chlorine has went back down.

The pool store practices 'dump and pray'. As such, they don't know what is safe and what isn't.

We use precision dosing that is appropriate per your CYA level, and our SLAM FC is less harsh than tap water. You need to be able to see the bottom well enough to rescue a swimmer if needed, and FC between min and slam. If so, hop right in and nobody will know.

Many of us go to SLAM for parties and nobody is the wiser. They might even remark how nice it is with no chlorine in the pool.

 

[JimMarshall]

The pool store practices 'dump and pray'. As such, they don't know what is safe and what isn't.

We use precision dosing that is appropriate per your CYA level, and our SLAM FC is less harsh than tap water. You need to be able to see the bottom well enough to rescue a swimmer if needed, and FC between min and slam. If so, hop right in and nobody will know.

Many of us go to SLAM for parties and nobody is the wiser. They might even remark how nice it is with no chlorine in the pool.

I routinely bring my pool to SLAM level ahead of parties. Everyone always talks about how it's the least smelly pool and want to know how I keep it clear with so little chlorine

 

[SloppyJosh]

My reagents came in yesterday.. I went ahead and started the SLAM last night. I overshot the FC just a bit and brought it up to 17. This morning it was down to 10.2 with .4 CC. Does that seem plausible? Seems like a huge drop.

I'm pretty certain of the results. I tested twice yesterday before adding chlorine.. I got FC of ~9.5 pool math app said to add just under a gallon of bleach.. I went ahead and put the full gallon in it. Went out about 45 min later and tested FC again and got 17.

This morning I tested twice.. once at .2 resolution and then again at .5 just to confirm because it seemed like such a large loss of FC. I added just under a gallon this morning, then went out to test again at 3:00 and it was down to 10.. Another gallon added.

Is this normal? Feels like I'm really blowing through the bleach. Also confirmed my CYA is where I think it is yesterday.. It is.. my SLAM target is 16.

 

[PoolStored]

Does that seem plausible?

Yep.

Testing and adding 2-3x a day is going to be a longer slam. Can you test and replace every 2-3 hours?

This is one afternoon...

Bleach.jpg

• PoolStored
• May 27, 2023

 

[SloppyJosh]

Yep.

Testing and adding 2-3x a day is going to be a longer slam. Can you test and replace every 2-3 hours?

This is one afternoon...

Bleach.jpg

• PoolStored
• May 27, 2023

Yep! I work from home and sit maybe about 50' away from the pool for most of the day.. I checked it at 7am, 10:30am (it had just dropped 1ppm at that point I added 24oz), 3:30PM, and will check again at 6, and probably 9.

 

[proavia]

Save your reagents and do the 10ml test for FC.
The 0.5 resolution is more than enough.

 

[SloppyJosh]

Things are looking really good. The water has been beautifully clear for several days.


Problem is, my chlorine consumption is still through the roof.

I checked my CYA again just to be sure and it had went up just a bit (I think maybe all my CYA hadn't dissolved last time I tested) So now I'm using 50 which puts my FC target at 20. I'm having to add .75 to 1 gallon of chlorine every few hours to keep it up there.

I've been slamming for over 7 days now. With the pool looking so good, I got to wondering what else could be causing the chlorine usage. I realized my ladder was probably holding a bunch of stagnant water. So I pulled it out and green chunks streamed out of the holes in the steps and supports. I've kept the ladder out for about 24 hours now.. so I'm hoping that was the issue and I'll start to see the FC stabilize.

I didn't do an OCLT last night but I'll be doing one tonight. Fingers crossed it passes. If not, I'm not sure what else could be causing the chlorine consumption like it is. it's overcast today and it just dropped 6ppm in 3 hours.