At first sign of algae ...

[ChasPro]

Each of the past 3 summers, my pool has "gone south" rapidly after the first signs of algae. Small whisps in a few spots on the bottom of my vinyl pool. I'd brush to encourage filtration or vacuum.

SWG, generally around 5-6ppm FC (0 CC). pH 7.6, TA 90-110. CYA 60-70. Pump running 10h per day. Sand filter.

My impression is that SLAM is for recovery when things go really wrong ... But I'm not sure what my first response should be when initial conditions emerge ... or what I should do after a heavy rain, if that opens the door to initial algae growth.

Some may say that my typical water balance is off, so start there. That would be helpful... to know which factor is most important above. My sense is that people will be commenting on TA/pH levels. I admit, I pay more attention to FC than those parameters... so maybe that's first.

And then, assuming water is balanced ... what would an initial action be if algae starts to appear in the future? For example, is a "small bleach shock" suggested ... to say 10ppm vs. SLAM ... like the pool store would suggest?

Puzzled at how rapidly a "perfectly clear pool" goes bad. Thanks.

 

[Texas Splash]

Algae prevention is all about the FC & CYA. The pH and TA do not control the potential for algae, only scale or stain control. So when preventing algae, it's important to ensure the FC is balanced to the CYA as noted on the FC/CYA Levels and that the FC never falls below the minimum amount listed. Remember that just because the water may appear clear, it doesn't mean excessive organics haven't already started growing. When in doubt, always do an Overnight Chlorine Loss Test.

Whenever you see algae or fail an Overnight Chlorine Loss Test, immediately go into a SLAM Process. No one-time shocks or short bursts of FC increasing. You have to maintain the proper (elevated) FC level for the SLAM for best success. Hope that helps.

 

[drsipe]

You can perform an over night chlorine loss test to verify algae, and if confirmed perform a SLAM, the earlier you catch the algae, the faster you can correct it.

Algae can only take hold when your chlorine level drops below minimum. Three days ago and seven days ago your FC was 2.8, which is below the minimum for a CYA of 60 or 70. I know it was barely below minimum, but algae is the enemy in the weeds just waiting for us to make a mistake, and it attacks. You might want to keep your free chlorine levels closer to the top of the target range.

 

[cledee]

Each of the past 3 summers, my pool has "gone south" rapidly after the first signs of algae. Small whisps in a few spots on the bottom of my vinyl pool. I'd brush to encourage filtration or vacuum.

SWG, generally around 5-6ppm FC (0 CC). pH 7.6, TA 90-110. CYA 60-70. Pump running 10h per day. Sand filter.

My impression is that SLAM is for recovery when things go really wrong ... But I'm not sure what my first response should be when initial conditions emerge ... or what I should do after a heavy rain, if that opens the door to initial algae growth.

Some may say that my typical water balance is off, so start there. That would be helpful... to know which factor is most important above. My sense is that people will be commenting on TA/pH levels. I admit, I pay more attention to FC than those parameters... so maybe that's first.

And then, assuming water is balanced ... what would an initial action be if algae starts to appear in the future? For example, is a "small bleach shock" suggested ... to say 10ppm vs. SLAM ... like the pool store would suggest?

Puzzled at how rapidly a "perfectly clear pool" goes bad. Thanks.

Like others have said in previous posts, at the first sign of algae, you need to take it to slam and leave it there until you pass all 3 test. Once you are losing 1ppm or less of chlorine at night, have .5ppm or less of CC and your water is clear.

 

[wireform]

One reason your having this is because your FC level is skirting danger. The target you should be having is the hotter end which is a FC of 10ppm. With your low FC the second it dips into minimum territory you don't know how long the SWCG needs to recover. The slam level for 70 CYA is 31 so 10 ppm of FC is a far cry to worry about. You need to do a slam and when done keep the chlorine level at the suggested 10 FC and you'll probably never see algae again

 

[ChasPro]

Thanks everyone. I think I was influenced by the standard pool FC guidelines that say somewhere between 3-4 is "safe" ... for humans and apparently algae. I was trying to stay between 4-5 to keep ahead ... but apparently that's actually behind.

I'll change strategy and pay better attention to the CYA-FC curve. Bought several gallons of bleach today, so SLAM it is.

With summer only lasting 3 months in Buffalo, a 2 week interruption to SLAM and recover is a good portion of the time ... so was trying to avoid that. Any advice on how to bring the FC down after SLAM is completed? Not chemically but through some other mechanism (like running the jet return at the surface to increase turbulence and aeration)?

 

[newdude]

Any advice on how to bring the FC down after SLAM is completed?

A few days of sunshine and some beverages.

SLAM is safe for people and equipment. So long as you can see the bottom, you can swim throughout.

 

[wireform]

You won't have a major issue bringing it down as that's a NO brainer. You stop adding and the daily FC loss takes over till you stop it.

 

[ChasPro]

You won't have a major issue bringing it down as that's a NO brainer. You stop adding and the daily FC loss takes over till you stop it.

Except in Buffalo where the overnight temps are mid-50s and the pool is partially shaded all day. Water temps are 68-72 all season. At the beginning of the season it took 2 weeks or more to drop from 2 gal of bleach dose to 8ppm.

 

[ChasPro]

ONLT of less than 1ppm while the FC is 6ppm and the pool is green.

No Cl added in this time period. SWCG has been off (out of service) for weeks, so these are bleach maintenance doses that I've been administering (if I didn't clarify that earlier and it has any bearing on advice).

This means that there isn't enough FC to work on the algae due to the current CYA levels?

 

[JJ_Tex]

ONLT of less than 1ppm while the FC is 6ppm and the pool is green.

No Cl added in this time period. SWCG has been off (out of service) for weeks, so these are bleach maintenance doses that I've been administering (if I didn't clarify that earlier and it has any bearing on advice).

This means that there isn't enough FC to work on the algae due to the current CYA levels?

If you are using bleach and your SWCG is off/broken, you should use the Non-SWCG chart. For a CYA of 70, your target range is 8-10 and SLAM level of 28.

Here is my colorful version of the chart if helpful:

 

[newdude]

SLAM is 40% of your CYA. I see from your notes you are purposely keeping it low to be able to swim. SLAM FC has a lower concentration of HOCL than tap water with 0 CYA and up to 4ppm FC. That's the part that feels harsh and SLAM is less harsh than taking a shower.

Swim away so long as you can see bottom well enough to rescue a swimmer, or be rescues yourself. (God forbid)

Except in Buffalo where the overnight temps are mid-50s and the pool is partially shaded all day. Water temps are 68-72 all season. At the beginning of the season it took 2 weeks or more to drop from 2 gal of bleach dose to 8ppm.

It doesn't matter how long the FC takes to drift down after. We see weeks long SLAMs all the time. It's no harm, just wait it out when th le time comes.

 

[ChasPro]

SLAM is 40% of your CYA. I see from your notes you are purposely keeping it low to be able to swim. SLAM FC has a lower concentration of HOCL than tap water with 0 CYA and up to 4ppm FC. That's the part that feels harsh and SLAM is less harsh than taking a shower.

Swim away so long as you can see bottom well enough to rescue a swimmer, or be rescues yourself. (God forbid)


It doesn't matter how long the FC takes to drift down after. We see weeks long SLAMs all the time. It's no harm, just wait it out when th le time comes.

Can't delete ... so I'm editing....

I was misreading @JJ_Tex chart above. I thought that Safe to Swim was only over the middle column, where it appears to be safe across the whole range, min to slam. Thanks.

 

[ChasPro]

If you are using bleach and your SWCG is off/broken, you should use the Non-SWCG chart. For a CYA of 70, your target range is 8-10 and SLAM level of 28.

Here is my colorful version of the chart if helpful:

View attachment 519317

@JJ_Tex ... Any info on why the overnight loss was low (below 0.5) with the green pool and reported FC level (around 6 ppm)? Is it the case that CYA "buffers the Cl from the sun" AND "buffers the Cl from 'functioning' until the FC is well into the recommended range"?

 

[duraleigh]

I don't want to start a debate, but ... What does "Safe to Swim*" mean on @JJ_Tex chart above if it is safe to swim at 24ppm?

It a common sense guide. Apply it along with your "common sense" and you should be able to find a good answer.

 

[ChasPro]

It a common sense guide. Apply it along with your "common sense" and you should be able to find a good answer.

Yes. I was reading the chart headings incorrectly. I edited my original reply. Thanks!

 

[ChasPro]

@JJ_Tex ... Any info on why the overnight loss was low (below 0.5) with the green pool and reported FC level (around 6 ppm)? Is it the case that CYA "buffers the Cl from the sun" AND "buffers the Cl from 'functioning' until the FC is well into the recommended range"?

Nevermind... The answer is, "Yes". Rereading the fundamental information on this site regarding basic pool levels, the definition of FC is a combination of both "free to oxidize" + "bound to CYA (buffered)" ... so at specific CYA levels the FC is only bound, not free to oxidize.

Feature Request: Yearly Refresher Quiz ... Take the test and if you get 100%, you're allowed to open your pool for the season. LOL

 

[ChasPro]

SLAM completed. Nice n clean. Thanks for the guidance.

 

[ChasPro]

I was a little leery of the final ONLT and clarity, so I SLAMed another day. Then heavy rain made the next night's ONLT suspect. Went one more day to have a full night without rain.

Much clearer this morning than yesterday... SLAM an extra day or more if you think you're clean. Possibly affected by heavy rain... but super clear is more than clean when you see it.

Not sure about ONLT ... was surprised when last night's reading was "so high" (27 when target is 24) ... possibly a miss count or some ghost drops (a bubble instead of a full drop... patience needed to fully reset bottle between each drop to get a correct drop). This morning's reading is closer to expected (21) ... but alas not conclusive with a 6ppm FC difference.

One more day ... ?

 

[ChasPro]

Having trouble getting consistent FC measurements... New test chems all around...

What's happening?


==========================================
ChasPro01
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Build Type: Vinyl
Volume: 13500 gallons
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Latest Test Result Summary:
FC: 26.5 (2 minutes ago)
CC: 0.2 (30 minutes ago)
pH: 7.6 (9 days ago)
TA: 100 (11 days ago)
CH: 110 (2 months ago)
CYA: 60 (9 days ago)
SALT: 3600 (2 months ago)
TEMPERATURE: 70° (9 days ago)
==========================================

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Test Results 08-12-2023 @ 09:00 AM
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Free Chlorine: 26.5
Combined Chlorine: minimal if any

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Test Results 08-12-2023 @ 08:35 AM
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Free Chlorine: 23.5
Combined Chlorine: 0.2

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Notes 08-12-2023 @ 08:34 AM
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47-48 drops = 23.5-24 FC
Less than 0.5 CC

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Test Results 08-12-2023 @ 07:54 AM
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Free Chlorine: 27.5
Combined Chlorine: 0.5

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Notes 08-12-2023 @ 07:53 AM
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55 drops = 27.5 FC

Sample taken from mid-depth with pump off overnight and some amount of overnight rain. Similar drastic difference between evening and morning tests, except the opposite of a couple days ago (high out of expected level in the evening and back to expected level in the morning... today the opposite).

All new DPD chems in the past week, so it should be consistent measurement recently. New R-0003 for CC testing today, so maybe better detection than prior tests with older chem.

Pump just started at 8am. Will test again in 30 min. Cloudy and sprinkling this morning, so hopefully not too much affect on ONLT attempt.

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Test Results 08-11-2023 @ 09:59 PM
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Free Chlorine: 21.0
Combined Chlorine: 0.0

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Notes 08-11-2023 @ 09:58 PM
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41 to 42 drops = 20.5 to 21 ppm FC

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Chemical Addition 08-11-2023 @ 02:22 PM
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+ 24 FluidOunces of Bleach

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Test Results 08-11-2023 @ 02:21 PM
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Free Chlorine: 22.5
Combined Chlorine: 0.0

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Chemical Addition 08-11-2023 @ 07:48 AM
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+ 40 FluidOunces of Bleach

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Notes 08-11-2023 @ 07:32 AM
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Much clearer this morning than yesterday... SLAM an extra day or more if you think you're clean.

Possibly affected by heavy rain... but super clear is more than clean when you see it.

Not sure about ONLT ... was surprised when last night's reading was "so high" ... so possibly a miss count or some ghost drops (a bubble instead of a full drop... patience needed to fully reset bottle between each drop to get a correct drop). This morning's reading is closer to expected ... but alas not conclusive with a 6ppm FC difference.

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Test Results 08-11-2023 @ 07:31 AM
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Free Chlorine: 21.0
Combined Chlorine: 0.0

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Test Results 08-10-2023 @ 07:53 PM
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Free Chlorine: 27.0
Combined Chlorine: 0.0

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Notes 08-10-2023 @ 12:19 PM
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SLAM another day due to rain, a possible slight haze in water, and morning losses greater than expected.

Should be no/minimal rain overnight.

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Chemical Addition 08-10-2023 @ 12:18 PM
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+ 24 FluidOunces of Bleach

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Test Results 08-10-2023 @ 10:14 AM
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Free Chlorine: 22.5
Combined Chlorine: 0.0

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Notes 08-10-2023 @ 06:30 AM
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SLAM
1) maintain 24ppm FC
2) Run filter until clear
2) CC less than 0.5
3) ONLT=~0 (pump off overnight)

Rain storm ongoing, so I took a sample from as deep as I could reach. Would prefer to have tested after some circulation and a dry overnight... so, will test once more after 8:30am to see what the combined loss will be (avg overnight plus rain dilusion).

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Test Results 08-10-2023 @ 06:25 AM
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Free Chlorine: 25.0
Combined Chlorine: 0.0

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Test Results 08-09-2023 @ 09:11 PM
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Free Chlorine: 25.0
Combined Chlorine: 0.0

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Chemical Addition 08-09-2023 @ 07:11 PM
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+ 24 FluidOunces of Bleach

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Maintenance 08-09-2023 @ 07:00 PM
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Vacuumed

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Chemical Addition 08-09-2023 @ 03:50 PM
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+ 24 FluidOunces of Bleach

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Chemical Addition 08-09-2023 @ 07:57 AM
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+ 32 FluidOunces of Bleach

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Notes 08-09-2023 @ 07:56 AM
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Mostly clear. Not much silt on bottom.

Will SLAM today to prep for ONLT, and vacuum this evening.

=====================