Thinking I Need to SLAM and the Rain!

[usdave1t]

So I have been battling with disappearing chlorine. I have an automatic chlorinator using 3inch tabs and have it set to 5 which is the highest setting. Tested my water last weekend and the FC was 0.5. Figured I would shock it so did that and the next day FC was at 5.5. A couple days later I was back at 0.5 and also noticed I had a few uninvited swimmers (water boatmen and / or back swimmers). This indicated that I had algae although there is no visible sign anywhere. I shocked the pool again and of course FC came back up.

We have had a few good days of bright sun and the pool sits in full sun pretty much the whole day. We have also had a LOT of rain recently so that too is playing havoc.

This morning I ran my tests again and these are my numbers:

pH = 7.6
FC = 0.5
CC = 0.0
CH = 250
TA =80
CYA = 60

Looks like everything is about where it should be with the exception of the FC. Also noticed I again have one or two of those uninvited swimmers (when I see these I skim them out and dispose accordingly)

So I am planning to SLAM the pool. Looking at the Chlorine / CYA Chart, looks like with a CYA of 60 I need to target an FC level of 24. Using pool math with my pool of 19600 gallons I need to add 957oz of 6% bleach to get to FC 24

I plan on using Walmart bleach (trip to Walmart coming up shortly). I will add the 957oz and then plan to test the FC every 30 minutes to 1 hour for the first few hours until I see FC loss slowing down at least.

Questions:
1. Does my reasoning and approach look reasonable? Any errors or omissions in my methodology (I plan on turning off my automatic chlorinator during the SLAM process)
2. It is currently raining very heavily here and there is a lot of rain forecast over the next few days. With all this rain I may not be able to SLAM it till next weekend. Should I put in a few gallons of bleach anyway just to try and bring the FC level up and keep adding it as needed over the next few days / week or is this a fruitless exercise. My thinking is some FC would be better than none, but is it just pouring money down the drain?

Thanks for all input and assistance - I have never SLAMed my pool before so want to be sure I am getting it right

Dave

 

[Texas Splash]

You have the right idea. Make sure on the calculator though that you manually update the bleach "WEIGHT" block and change it from 6% to 8.25% if you use Wal-Mart's Great Value (5 1/2 gallons). If you use Wal-Marts latest white bottles of 10%, update that as well (4 gallons 3 quarts). You can still SLAM even though you may experience some overflow or drain excess water. It won't be fruitless. We got pounded this morning and now the sun is out. Crazy. But do the best you can based on weather. Use your good judgment. Stay close to that SLAM page and you'll do fine. Good luck!

 

[Mr Bruce]

I would pull all those tabs out and not put any more CYA in any form in the pool. 60 is ok/good for Texas but any higher and you are asking for trouble.

Liquid bleach (chlorine) only.

 

[usdave1t]

Thanks for the quick replies. Heading off to Walmart now to pick up bleach.

Another question that came to mind: when I start the SLAM process i.e. add the bleach, how long should I wait before testing the FC? Do I need to allow time for full circulation, or just test after 30minutes?

Thanks again
Dave

 

[Texas Splash]

Depending on your circulation, wait about 20-30 minutes and try it.

 

[Mr Bruce]

Same difference. After 30 minutes you should be mixed pretty good. How does the water look?

 

[usdave1t]

So I purchased 8.25% Great Value bleach and as per pool math added 5.5 x 121oz jugs targeting FC of 24

Just tested the FC, 45 minutes after added bleach to the pool and it came back as 34.

Two thoughts I have:
1. The bleach hasn't fully mixed in yet although I have the pumps running on high so wouldn't have thought that was the problem
2. What I purchased as 8.25% bleach is actually something stronger?

Anyway, plan now is just to test again in about an hour and see where we are that then. Once FC drops to 24 I plan to hold that (add more bleach if needed) and then do an overnight FC test

I think I am right in saying if I don't lose any FC overnight then I am good and can let the FC drop to normal (for my CYA of 60, I should be targeting FC =7


Also, Mr Bruce, why do you say that a CYA higher than 60 in Texas is going to cause trouble?

Thanks again
Dave

- - - Updated - - -

Same difference. After 30 minutes you should be mixed pretty good. How does the water look?

And the water looks good - very clear. There is no sign of any algae that I can see. I did see two backswimmers this morning - of course should now be removing their food so they will go away

Thanks
Dave

 

[RobbieH]

Did you change the % of the bleach in PoolMath from 6 to 8.25?

The higher the CYA, the higher FC must be. And then if you have a problem, you must use MUCH more bleach at 60 than in the 30-40 range. You can live with 60, you just don't want to get (much, if any) higher.

 

[Mr Bruce]

Perhaps I worded it poorly. You can definitely run a CYA of >60, but if you use those pucks all season you will have very high CYA by August and will have a very hard time keeping the FC above minimum.

 

[usdave1t]

Did you change the % of the bleach in PoolMath from 6 to 8.25?

I did yes. Only explanation I can think for the high FC is that the bleach is actually stronger than the 8.25% it says on the bottle?

The bleach I purchased says Active ingredient Sodium Hypochlorite 8.25%, other ingredients 91.75%. Yields 7.86% available chlorine. Contains no phosphorous.

I seem to remember reading somewhere that someone bought some bleach that was stronger than it said on the bottle?

Thanks
Dave

 

[Mr Bruce]

The other possibility is your pool is smaller than you think.

 

[usdave1t]

The other possibility is your pool is smaller than you think.

Thought you were on to something there especially when I went and measured my pool again. Width and length of the main pool (it is rectangular) were both slightly less than I thought. There is then a sun shelf at each end and the spa. Overall my volume calculation was out by just shy of 1000 gallons. Revisiting PoolMath tells me I should have added 5.4 x 121oz jugs rather than 5.5 jugs. Have to admit to eyeballing the half a jug although don't think I was far off.

Would an extra 12oz or so of bleach really result in such a high FC reading?

Thanks
Dave

 

[RobbieH]

No, we eyeball stuff all the time here, especially bleach.

 

[Mr Bruce]

Not that high. Another possibility is you tested in a dead spot. After the next add I would collect a sample from a few different places and compare. There's no way you got some batch of crazy strong bleach.

 

[usdave1t]

OK so just retested in 3 different spots as suggested:

1. Deep End near to the return to ensure it is not a dead spot FC = 29
2. Deep End opposite side also near return FC = 29
3. Shallow end near where the spa overflows into the pool FC = 31

Seems pretty consistent.

I plan on letting the FC drop to 24 which was my original target and then holding it there and doing the overnight test to see where I am at

Thanks again for all the help

Dave

 

[usdave1t]

About an hour later than previous post and FC now at 27. We have got partial sun at the moment so I guess that is eating some of the FC. As I said above I plan to target holding at 24 once we get there. Looks like about another hour we should see 24 or 25. May have to add some more bleach to hold it at 24 until the sun goes down and then will do the OCLT

Think I am heading in the right direction now

Dave

 

[usdave1t]

OK would appreciate some more input here. I am confident in my pool volume calculation (18627 gallons - pool consists of all rectangles and squares so no complex shapes to calculate).

Tested FC at 4:30pm yesterday and it was at 22. My target is 24. PoolMath told me to add 60oz of 8.25% bleach which I did. Tested at 7:00pm and FC was 30. No idea why it went so high!

Tested this morning before sun rise and FC was 21 so definitely something in the pool that shouldn't be. PoolMath told me to add 83oz of 8.25% bleach so have done that but i am expecting the FC to go high like it did before. And thoughts on why it would go high?

Is it possible that PoolMath is giving erroneous data using it on a Mac computer - don't see why it would since it is web based.

Only other thought I have it that for the FC test I am using a 5ml sample and counting each drop of reagent as 1.0 rather than 0.5 - I read on another post that this is OK to save on reagent?

I will test FC again shortly and post the result.

My next plan if the FC still comes in high would be to figure out from my results what volume of bleach gives me an increase of 1 on FC and calculate my needs by hand?

Thanks again for the help
Dave

 

[Mr Bruce]

It's either testing error, pool size miscalculation or circulation. But I don't think it's that important to solve right now. If it were me, I would just round down to the nearest 1/4 bottle of bleach and not spend too much time on it right now. Once your SLAM is over maybe do some more experimenting.

How's the water look?

 

[Texas Splash]

Good morning Dave!

And thoughts on why it would go high?

Well, I'm not real clear on the relationship between Windows & MAC platforms, but I would be surprised if that was an issue. Generally FC increases are a result of one or more of the following:
- Wrong pool volume entered in the calculator
- The "WEIGHT" field not updated manually on the calculator on the FC row
- Adding more bleach that required
- Not allowing bleach to mix adequately before testing and/or testing from different locations each time
- Testing error

Testing error is the one that grabs my attention most only because the 5 ml just isn't as precise. We do recommend it for those who have a long SLAM ahead of them, or perhaps are almost out of R-0871 drops, but typically the 10ml sample is best. It's also important when evaluating overnight loss to not be too high over the SLAM FC level. I know it was an accident, but from personal experience I found that even in a clean pool if I went too high, I could still experience excessive FC loss - more than the 1 ppm nightly limit.

 

[usdave1t]

It's either testing error, pool size miscalculation or circulation. But I don't think it's that important to solve right now. If it were me, I would just round down to the nearest 1/4 bottle of bleach and not spend too much time on it right now. Once your SLAM is over maybe do some more experimenting.

How's the water look?

Well I am confident in the pool size calculation. My pool and spa is all rectangles and squares so its not a complex calculation. I also went and measured the depth to ensure it was what I actually paid for! I am running the pump 24 hours during the SLAM process so don't think it can be circulation.

That leaves tester error. Didn't think I was doing anything wrong there but will try testing with a full 10ml sample and see what I get.

Pool water is clear although I did see this morning I still had an uninvited swimmer (water boatman / back swimmer!)

Thanks again
Dave