Pool Math SLAM additions accurate?

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goody222

goody222

Silver Supporter
Feb 6, 2018
184
Chesapeake, VA
Pool Size
21000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-15)
Chemistry as of yesterday with Taylor 2006:
pH= 7.2
FC= 3.5
CC= 0.0
TA= 60
CYA=around 60-65
Calcium = 180

Clear water, CC of 0.0 BUT a few times in the past 2 weeks found algae growing on the wall which I immediately brushed. I didn't perform the overnight test due to process of elimination.
Pool has been scrubbed, skimmed and vacuumed.

When I put all the numbers in pool math to for a FC target of 28 with a 25,000 gallon pool, I get 5 bottles of 1 gallon 12.5% liquid shock (which I confirmed on the label) which I added. 2 hours after add, FC is only 17.5ppm! 3 hours after add (10pm, dark out), same thing. Then, first thing this morning at 5:30am (still dark), I get 17.0ppm! I'm measuring exactly 10 ml, using a speed stir, 3 level scoops of powder and adding drops greater than 1 drop per second.
Any ideas what could be going on? Thanks!!!!!
 
Pool math is as accurate as you are, there is a phrase; junk in, junk out. If your gallons is correct and your bleach you add in is fresh, it will be correct.

So there is two possibilities, your gallons or the 12.5% that degrades rather fast was old.

If your other additions such as acid or daily FC are rather correct, it was the bleach.

Cya is measured in 10's, so would call your cya 70 untill you do your normal cya retest
 
For your FC level, perhaps chlorine you added was a bit old and lost some of it's potency. What was date code on bottle? I was at a Lowes recently and saw many cases there with 017-347 date code, so even if you just bought the chlorine it could be past it's prime.

Also, 3 level scoops of powder is excessive, especially for 10ml test. You only need 1 scoop for 10ml test. More powder doesn't give more accurate test result, just wastes money.
 
I just purchased the liquid shock 3 days ago at Leslies - I assumed a pool store would have up to date shock. I'll check the dates when I get home from work.

Also, I was adding 3 level scoops because I had read that you need more powder for very high FC testing or you will get an inaccurate result.
 
You only need enough powder to turn the sample pink. If it flashes pink and goes clear add another scoop. If two scoops don't turn the sample pink, either there is no FC or it is extremely high, and I would test a 1:1 diluted sample to get a ballpark estimate of FC at that point.
 
Ah, OK! that makes sense. I'll keep it in mind. It hasn't been a problem so far since I seem to go through drops faster than the powder.
 
I have never had poolmath give me a wrong answer. And the Effects of Adding Chemicals part has also been spot on (Aside from the pH, which is only good for a narrow set of parameters and which has a disclaimer.) I get the same dose you do when I plug numbers in.

So it's either weak bleach, or you had some ammonia that used up a bunch of chlorine really fast, or a testing error.

It wouldn't surprise me if Leslies sold you some old bleach. The store near me keeps it hidden out of sight and they really discourage you from buying liquid chlorine. Their's probably doesn't turnover real fast. And also, bleach jugs are heavy. I could see some part-time kid just stacking the new on top the old rather than expend the effort to restack it all right.
 
goody222 said:
I just purchased the liquid shock 3 days ago at Leslies - I assumed a pool store would have up to date shock. I'll check the dates when I get home from work.

Also, I was adding 3 level scoops because I had read that you need more powder for very high FC testing or you will get an inaccurate result.
Click to expand...
One scoop should do the trick. I've tested mine up to 28ppm, no problem. If I recall it's accurate up to 50ppm.

I didn't expect Lowes to sell old stuff either, first time I was at that particular store, but guessing as new stock came in they just stacked on top. Could be same for any store. I always check dates and get the freshest I can find.

If dates do check out, then either testing error as starting point, the testing powder is past it's prime or perhaps your pool gallons is more than you thought?
 
OK - it must have been the chlorine from the pool stores that I just purchased. Today I got regular bleach at Walmart (June '18 date code) and added exactly what pool math said and I got the correct results!

Neither liquid shock bottles (all purchased 3 days ago) had a date code I could read. I called the liquid shock company from Leslies ("Super Shock") and gave them the location/lot # and they are going to call me back at some point to let me know the date. My local mom/pop pool store sells "Shock-It" and I can't find anything on google about it - not even the manufacturer. Only thing on the bottle says "1720670PA-1 08:23(6)"
 

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UPDATE:
So Leslie's (at least in Chesapeake, VA) sells "SUPER SHOCK" as their liquid chlorine. The lot sticker on mine was "175 02". The 17 is 2017 and 5=May. So OVER 1 year old. I called the manufacturer to confirm this. He was really sorry and is going to mail me a check.

My local Mom and Pop Pool store sells "SHOCK-IT". Their label has "1720670PA-1 08:23(6)" on it. 17=2017 and 206=206th day of the year.

A good lesson that even though the store may have just ordered it, it may have been sitting in a stock room for months or years. So I went to Walmart, paid $1.77 for 6% bleach. Date code = 18 183. Perfect.
 
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