Do I need to SLAM? Please help.

[Sharla]

We’ve had a lot of rain in the last couple weeks and my chlorine level has bottomed out.

SATURDAY: (tested by fancy machine at pool store)
FC: .03
pH: 8.0
Hardness: 320
TA: 80
CYA: 40
(Salt: 2400, set at 15%)

I used the pool math calculator and added 24oz muriatic acid, 96oz of 6% bleach, 2 bags of salt, and an unmeasured amount of baking soda (just threw some in ). I’ve never needed to SLAM before and I expected this amount of bleach and other chemicals to basically fix things. I tested again today, thinking I would just need to fine tune things like pH, TA, CYA and SWG settings. Nope.
The chlorine is still way off.

MONDAY: (tested by me at home)
FC: .5
pH: 7.8
Hardness: 300
TA: 95
CYA: 40
(Salt: 3115, set at 25%)

My pool water still looks clear. Do I need to SLAM?

Should I SLAM or just add what pool math calculator says to add (75oz of 6% bleach, 19oz muriatic acid, 13oz baking soda, Zero CYA stabilizer, 10lbs salt) and then turn up my SWG percentage?

If I need to SLAM, I’m having trouble understanding the chart for my target FC and Shock FC levels. The SLAM directions say that the ideal CYA level for a SLAM is 30-40, but the chart for SWG pools says SLAMing at CYA levels as low as 60 is not recommended. My CYA is 40. Do I raise the CYA before SLAMing? At the bottom of the screen for the pool math calculator, it says “Shock: 16” so is that the target number for my shock level if I SLAM? Has that number already taken into account the fact that my CYA is 40?

*****edit*****
Problem solved! I did the math wrong. My FC is not .5, it’s 5!!!

 

[Dirk]

A TFP expert should be along in a bit. But based on what I'm learning here, and if you're running a SWG pool, your CYA is low, which might account for the chlorine loss. Have a look:

Pool School - Chlorine / CYA Chart

The way I'm reading the charts, you need to be at 70 for CYA. (I'm adding CYA as we speak, getting ready to fire up my own SWG.)

Why do you think you need to slam? Is the water murky? Any algae forming?

Also, SWGs struggle to move FC by any great amount, they basically just maintain it. So you use liquid chlorine to get to where you need to be quickly (before you really do get a problem), then fine tune the SWG to maintain the level. Test everyday through this process to maintain your target FC, tapering off the liquid chlorine as the SWG takes over.

 

[Dirk]

Oh, I think you're struggling with the same thing I am. The Pool Math calculator should really have a "SWG" checkbox. I believe the stated goal for CYA of 30 to 50 is for NON-SWG pools. CYA should be higher for SWG pools, as per the the Pool School - Chlorine / CYA Chart.

I've been taught here to use the target FC as the minimum, and to ignore the stated minimum. That way you have a little cushion should you slip up or if the pool gets "surprised" by weather or a pool party (extra bather load).

Wait for a TFP expert to confirm all this, and I'll be following along as I ready my pool for SWG.

 

[Dirk]

I tried to look up your test kit, but apparently no pools are being tested these days with Oreos! Was that supposed to be OBO test kit? The TFP expert will advise you to get a better test kit, especially before you embark on any slamming. There's also something going on with your pH, and TA. If you added 24oz of acid, your pH and TA should have been lower the next day. What strength acid are you using? Or, again, it might be your test kit...

--edit--

Could have been the baking soda...

 

[Sharla]

Thank you so much for your quick responses! I figured it out... This is hilarious and rather embarrassing. When I did the FC calculations today, I multiplied by .05 instead of .5 so that’s why I thought my FC was still low. Hahahaha!!!

I do not need to slam. Everything is fine! The bleach I added two days ago did its job. My FC is not .5, it’s 5. All I have to do now is wait for it to come back down. Oh, my goodness. I feel so silly but also relieved.

 

[Sharla]

I tried to look up your test kit, but apparently no pools are being tested these days with Oreos! Was that supposed to be OBO test kit?

Oreo! I didn’t notice it said that! I’ll change my signature in a few minutes. When I set up my signature, I was using the test kit my pool builder gave me, which was Oreq. It guess it autocorrected to Oreo. Now I use the recommended FAS-DPD. Thanks for your responses!!!

 

[kimkats]

Hi! I am so glad you figured it out!! Good job! Been there done that more times than I care to remember

Like Dirk said, in the future when you need to raise the FC up use liquid chlorine/bleach (same stuff just different %) then allow you SWG to take over.

Now lets see if this helps you and Dirk with Pool Math......go all the way down to the bottom...........set it up down there for your pool----TFP method, SWG for FC and something else I already forgot. See if setting that up helps with the confusion. Please let me know so I can learn with you.

Kim

 

[Sharla]

Dirk, I thought I needed to slam because I added 96 ounces of 6% bleach and my FC only moved from .3 to .5 ....BUT then I realized I had done the math wrong. I multiplied 10 by .05 instead of .5. My FC is 5 and all is well except for my math skills. Haha!

- - - Updated - - -

Thank you, Kim. Yes, I used 6% bleach and it worked perfectly. The only problem was with my calculations. I’ve got it straight now! Thanks for your response! I’ll take another look at the settings on the pool math calculator per your suggestion. Thanks!!!

 

[Dirk]

Now lets see if this helps you and Dirk with Pool Math......go all the way down to the bottom...........set it up down there for your pool----TFP method, SWG for FC and something else I already forgot. See if setting that up helps with the confusion. Please let me know so I can learn with you.

I don't see anywhere you can enter SWG. I think all the suggested ranges are based on non-SWG pool... No?

--edit--

Scratch that, I found it, and it does affect the CYA range. Thanks Kim!

 

[Dirk]

Oreo! I didn’t notice it said that! I’ll change my signature in a few minutes. When I set up my signature, I was using the test kit my pool builder gave me, which was Oreq. It guess it autocorrected to Oreo. Now I use the recommended FAS-DPD. Thanks for your responses!!!

FAS-DPDeeee, yah babieeee! (Well, almost rhymes...)

 

[cfherrman]

Stop adding baking soda, you do not need to raise your ta when you are lowering your ph

 

[triptyx]

Stop adding baking soda, you do not need to raise your ta when you are lowering your ph

This, thank you cfherrman. TA is what I call a "magic" number - as long as it's above 40 or so, and you're not seeing unexpected / wild large swings in your pH, it's fine wherever it is. Don't work to try and keep it at 100 or so, you'll just be chasing pH and TA all season! Only consider adding baking soda if it falls below 50.

If you ever think you might need to SLAM, you can always perform an OCLT test to know for sure:
Pool School - Perform the Overnight FC Loss Test (OCLT)

This test can help you to set your mind at ease if you're seeing some odd/unexpected chlorine consumption.