Post-slam, advice on first steps without tabs

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survivalcar

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Jun 9, 2018
58
Northampton, MA
Thank you all for your help getting me through the SLAM. The pool looks great and I just took some measurements I wanted to post to ask for advice. First of all, it seems to me that the FC dropping from 28 to 7.5 happened faster than it should have if the sun makes it go down 2ppm/day. It passed the FC loss test and no one's been in it yet so the sun is the only factor.

As of today:

FC = 7.5
CC = 0
pH = 8.0
TAC = 120
CYA* = 60

*I'm still not sure I'm reading the CYA right and maybe I'll invest in the kind of kit our pool guy has, where you poke the dipstick down until you can't see the dot. FWIW, the strips show CYA somewhere between 0 and 50.

According to this chart (Pool School - Chlorine / CYA Chart) my FC is within the ideal range for a CYA of 60. So, given that I'm going with chlorine shock instead of the pool tabs (thanks for the advice) I assume that, for example, today I might throw in slightly less than a half gallon of shock (a half gallon would raise FC 2ppm, for a 30,000 gallon pool), in anticipation of the FC going down to 5.5 or lower by tomorrow. Am I on track so far?

And I have stuff to adjust the pH and TAC. When should I start that?

What other things might go askew once I try to adjust the pH and the TAC? Anything I should watch out for?

Thanks everyone for this great resource.

Chris
 
Lower your pH to 7.4 or so with muriatic acid. That will drop your TA a touch. When the pH rises to above 7.8, repeat.

Add your 2 ppm FC worth of LC and test tomorrow. You may need to adjust that depending on bather load, etc.

Your FC dropped from SLAM level quicker as the UV impact on FC is greater at SLAM level than target level.

Should be no impact to anything by adding MA for pH adjustment.
 
We do not recommend long term use of sodium bisulfate. But, if you have some, it can be used but please switch to muriatic acid when possible.

Sulfates can build up in your pool water and damage pool equipment. It is especially hard on SWCG's. Which you do not have.
 
survivalcar said:
Thank you. I just realized to lower the pH I have Sodium Bisulfite and not Muriatic Acid. Does that matter?
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Since you have the bisulphate, use it up. Just don't buy any more.

The FC loss sounds normal. The higher the FC, the greater the percentage that burns off. It's not a fixed ppm per day, or we'd be able to add a week's worth of chlorine once a week. And it's not even a steady percentage. You might drop from 20 to 10 in less time than from 3 to 2.
 
I must be doing something wrong. Seemed to me it took 5 drops to bring the color on the pH reading from 8.0 down to 7.4. Reading the chart to reduce the pH using Sodium Bisulfate, it says 3.85 lbs of SB per 10,000 gallons, which means I'm looking at adding 3.85 x 3 = 11.55 lbs of SB. I don't think I have that much, and anyway on the side of the SB bucket it says 2.5 cups per 10,000 gallons if the pH reads 8.0. That means 7.5 cups, which is 3.75 pounds.

What am I doing wrong?
 
What is your TA? That is needed to determine how much acid to add.

- - - Updated - - -

Sorry - TA of 120.

Poolmath is showing 139 oz (by volume) of dry acid for that pH drop.

My numbers on Dry Acid are wrong. I had an errant Borate number in my PoolMath calculator.
 
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survivalcar said:
I must be doing something wrong. Seemed to me it took 5 drops to bring the color on the pH reading from 8.0 down to 7.4. Reading the chart to reduce the pH using Sodium Bisulfate, it says 3.85 lbs of SB per 10,000 gallons, which means I'm looking at adding 3.85 x 3 = 11.55 lbs of SB. I don't think I have that much, and anyway on the side of the SB bucket it says 2.5 cups per 10,000 gallons if the pH reads 8.0. That means 7.5 cups, which is 3.75 pounds.

What am I doing wrong?
Click to expand...
Plugging numbers into poolmath. I get 84 ounces by weight or 56 ounces by volume. That's 7 cups as opposed to your 7.5 cups. So you're not doing anything wrong.

Add half and see where it gets you. If you need more, add it. You'll know within an hour or so, especially if you brush a little to help mix things.
 
I have to learn how to use this PoolMath, I'm sorry I didn't see that before. Still I think that's more than I got. I assume the equivalent reduction doesn't require as much MA?

- - - Updated - - -

OK thank you, I'll start with half and re-measure. In the meantime I'll read up on the Poolmath.
 

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The dry acid does nothing to the FC in the pool.

Was the pump running after adding the LC and dry acid?
 
Yeah it runs 24/7, or at least until I can get a timer.

I did the measurement twice both times. The only other thing that might account for the difference is there's no daylight here and I was taking the measurement by lamplight. Maybe one of them is incorrrect

Also the pH is now down to 7.4
 
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