Question about SLAMming a swim spa

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AndrewFH

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Jul 30, 2013
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I developed some cloudy water and my CC was pretty high, so I thought I would try the SLAM process.

Test results before:
FC 3.38
TC 6.87
pH 7.2
CYA 74 (I know it is high and is from prior use of dichlor before I knew better)
I applied 57 oz of 8.25% bleach per the Pool Calculator. This should have raised FC to 30ppm (per Chlorine/CYA Table).
I checked again in just over an hour and got these results:

FC .45
TC 4.81

Is this a normal response during a SLAM? A 30ppm drop in FC in an hour?
I assume if so it means there really is something going on in my water that the chlorine is killing.

I added more bleach to get the FC back up to 30ppm. This time I checked the FC level about 10 minutes later just to see if it was actually getting up to 30ppm. Discovered my test kit only reads up to 10ppm. It did show "Hi" as the reading so apparently all I can confirm is that it was above 10ppm.
 
You have very high CC, so clearly there is something in the water rapidly consuming the chlorine.

How are you testing? ... clearly one of the recommended test kits would be a good idea with the FAS-DPD test ... or just drain and start over.
 
There are quite a few discussions about that tester if you want to try a search ... ok for some things ... worthless for others. One major limitation being what you just discovered.
 
I plan to get a better test kit, but can't till later. As to my original question, is that kind of drop in FC (30ppm in about a hour) possible? Does algae (or whatever is using up my chlorine) use it up that fast?
 
I have a follow up question. I have been continuing this process which was started two days ago. As noted earlier, I don't have the ability to test above 10ppm so I've been "overshooting" the shock level of the chlorine to ensure it is high enough.(Chlorine/CYA chart says based on my CYA of 74 it should be around 30ppm, I have been adding chlorine based on putting in a level of 40ppm in the pool calculator). Because of my work schedule, I generally am only able to check the level and add chlorine twice a day (once in the morning and then again in the evening). The level is typically around 5-10ppm each of these two times.
This morning it was at FC 6.7 and TC was 7.5 (making CC .8). This is down from last nights reading of CC of .8.
The water is much more clear.
Sounds like I may be near the end (here's hoping).
Would you agree? Anything you see I need to do different?

As I understand it, the three "conditions" I need to meet to know the SLAM is successful and can be stopped are:
1) CC is 0.5 or lower (this is getting close but not there yet)
2) You pass an OCLT (I am obviously still using chlorine overnight although I can't tell exactly how much due to the limitations of my test kit)
3) And the water is clear (the water is very clear now)

I am assuming the reason for the OCLT condition is that if I am losing more than 1ppm of FC overnight, there is still something in the water that is being killed/cleaned by the chlorie...correct?

My spa is covered (under a deck) and gets no (or if any, it is very slight) exposure to sunlight. If (when) the SLAM is successful and I am no longer consuming chlorine, how do I get the chlorine level down (if it is too high at that point). Will the chlorine dissapate without exposure to sunlight and nothing in the water consuming it?

Thanks.
Thanks.
 
AndrewFH said:
I am assuming the reason for the OCLT condition is that if I am losing more than 1ppm of FC overnight, there is still something in the water that is being killed/cleaned by the chlorie...correct?

My spa is covered (under a deck) and gets no (or if any, it is very slight) exposure to sunlight. If (when) the SLAM is successful and I am no longer consuming chlorine, how do I get the chlorine level down (if it is too high at that point). Will the chlorine dissapate without exposure to sunlight and nothing in the water consuming it?

Thanks.
Thanks.
Click to expand...

You are correct, the point of the OCLT is to eliminate the sun as the source of loss. Sounds like you are still loosing a LOT of chlorine, so I do not think you are as close as you think you are ... CC are only one of the criteria as you know.

It is safe to swim up to shock level for your CYA, so it really does not matter how long it takes to drop.

I am just not sure how you will ever test the CC and the OCLT criteria without the FAS-DPD test. BTW, the CC criteria is really < 1 drop ... that means the CC should really be below 0.2ppm to pass. Usually the CC should be very nearly 0ppm or it is too high.
 
The ColorQ 7 uses a DPD test. I know the difference between OTO and PDP, but not sure what the difference between DPD and FAS-DPD is. (I do know the difference in terms of how you actually do the test as I have read the instructions for the TF100 test kit, but I don't really know the difference between the chemistry of the two methods).
The ColorQ 7 tests for FC and TC (with CC being the difference between the two). So I assume (maybe incorrectly) that if the FC and TC read the same, I will have reached zero CC. And as far as the OCLT, I should be able to tell if I lose more than 1ppm FC overnight.

I plan to continue until I reach zero CC (as opposed to just less than 5ppm).

You comment that "it is safe to swim up to shock level for my CYA"...the one question I have in that regard is this: As long as the CC is over 5ppm (or really 0ppm), there is obviously "something" in the water that is still consuming chlorine. My wife's concern is that there is bacteria or something else potentially harmful (she is very prone to getting infections). Is this a valid concern? What are the possible reasons the chlorine is still being consumed at such a high rate?
Also although it is safe, will it bleach out swimsuits, etc. at shock levels?
 

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There is something in the water, certainly, is it dangerous ... maybe. I meant it is safe up to shock level AFTER you have passed the 3 criteria. And it will not bleach out the swimwear as the active chlorine is still lower than you would find in an unstabilized public pool with a FC of 2ppm.

The OTO and DPD tests require color matching. Humans can not differentiate a 0.5 difference in the color ... and I would not trust a computer to do it either. The FAS-DPD allows you to count drops with a resolution of 0.2 or 0.5ppm ... it is much more accurate than the OTO or DPD tests.
 
Lightbulb just went off and I get what you mean about my test kit and the CC and OCLT test. I did a test for FC and then did the test for TC without adding the reagent for the TC test (this kit uses the same sample and you add a reagent to the FC sample and it tests the color change). Should have gotten the same result, but it showed that the CC was .09.
I guess I will be going ahead and getting a different test kit (good thing I have a credit card).
 
I've gotten a TF100 test kit so I can get a better reading of the chlorine. CC has been down to zero (no color change) last few days, but still not under 1ppm chlorine loss over night. It is down to 1.5ppm pretty consistently. Is is possible that with the ozonator in the spa this is as low as it will get overnight, or should I keep going with the SLAM until it is less than 1ppm loss?
 
If you can't turn the Ozonator off it's going to eat some of your FC and you'll never technically pass the OCLT.

You could run the unit and bring the FC to shock level and then shut the unit off, wait 15 minutes and test the water without the unit on. Get up the next morning and test it again before turning the unit on. While not ideal, it may have to do in your circumstnace.
 
Unfortunately there is no way to shut the ozonator off (except possibly disconnecting the wiring from it). I guess I could shut the power off to the spa, but then pumps, filters would also be off all night.
 
I would turn everything off and run the test. Wait about 15 minutes after you shut it down to test the FC. As I said, it's not ideal but with no way to shut the Ozonator down you really don't have a choice if you want to pass the OCLT.
 
This is why for a spa it's better to get to know one's baseline 24-hour chlorine loss and use that as the determinant that one does not have unusual chlorine demand. Without an ozonator, a hot spa typically loses 25% of the FC over 24 hours while with an ozonator it can be 50% or more. The OCLT criteria doesn't work well in these situations between the hotter water and an ozonator.
 
Overnight last night my loss was only about 10% (dropped from 15.5ppm to 14ppm) with the ozonator running so it sounds like I may be good as far as ending the SLAM. I will turn the power off overnight and do one more check to confirm if it is under 1ppm loss. Once I confirm that, and get it back down to normal FC levels, I will monitor with the ozonator running to establish a baseline.
Does this sound like a good plan?
Thanks for all the help.
 

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