SWG produces Chlorine but is absent from pool

[Phil3157]

Everything regarding the SWG is working in theory, i.e., meter at 100%, bubbles being produced, salt over 4000ppm, but zero chlorine in pool. I removed the cell today and filled a bucket from the pool which I placed the cell into it and connected the terminals and turned it on. (I had put an old cell into the SWG housing while doing this) I let it run for a minute or two and the water turned cloudy. I then drop tested the water in the bucket and the sample turned beyond yellow to orange, ie., chlorine production off the scale! I reinstalled the cell unit to its inline plastic casing and again took poolwater samples at each of the entry points into the pool and sure enough - zero chlorine as before!
If the SWG was pumping water through an underground leak my water level would have gone down as I have had the autofill turned off for a week or so. I had previously loosened the endcap of the SWG and sampled the water leaking which showed no signs of Cl. I was unable to test it at the other end of the plastic housing as the cap was either molded or cemented on. However if somehow there was a blockage in the lines and the water was circulated by- passing the poo,l then surely I would have found some trace of chlorine when I tested it at the leaking endcap? This is driving me crazy as there does not seem any logic to it. I really would appreciate any ideas as to what may be going on.

 

[DBfan187]

did you do a full analysis test your water? could you please post the results?

 

[dmanb2b]

Your SWG is likely fighting an algae bloom or your CYA is too low...it's a guess, but we often see this when organics are present and the SWG just can't keep up with the FC demand. You should supplement with liquid chlorine until you are able to get an FC reading and then perform an overnight FC loss test with the SWG turned off. If you lose more than 0.5ppm fc overnight, you should shock the pool with liquid chlorine.

 

[Phil3157]

I had drained and refilled two weeks ago. My last readings were: Cl=0, PH=7.4, TA=120, CYA= 40, Salt =4100ppm, Hardness = 200. I know the CYA is about 1/2 of what it should be, but I had put in 4# five days ago (pool is approx 13k gall). From past experience it has taken 10 days or so to get an accurate CYA reading. Anyway the issue is that when I did the "bucket test" it was with water taken straight out of the pool, complete with low cya etc. The only difference I can think of it it was from the top of the pool whearas water going to the filter is coming off the bottom. Pool water temp 6" under surface was 71 and on the bottom I would guess it to be 2-3 less.

 

[dmanb2b]

If the pool water has been circulating and the SWG is generating, you should be able to get and FC reading from water taken near one of your returns. I would add liquid chlorine tonight and perform the overnight FC loss test to rule out organics

 

[Ranger987]

It's sometimes a hotly debated topic, but have your water tested for phosphates as well. Most mfgrs recommend a phosphate level as close to zero as you can reasonably get. Phosphates have been shown to deplete chlorine rapidly. You're already adjusting the cya, so I'd look at a phosphate remover if your level is high. If you've had heavy algae in the past year, or if you get a lot of organic debris, this might be part of the puzzle.

 

[dmanb2b]

Phosphates have been shown to deplete chlorine rapidly.

That is an incorrect statement Ranger. Phosphates are a nutrient for algae. If algae has already broken out, the pool needs to be shocked. You can try using phosphate remover once you have killed all the algae in your pool water, with chlorine, as this may slow down future outbreaks, but adding phosphate remover now will not kill algae, nor will it slow down chlorine consumption. There are many who operate SWG pools with phospahte levels in excess of 3000.

You can see this recent post where this was once again debated

phosphates-t29275.html

 

[Bama Rambler]

How did you get those test results?
You need to run all the test again and post the numbers and tell us which test you have.

As Dman said, don't worry about the phosphates. True enough it's food but, if there's nothing there to eat it, it doesn't matter.

You can also crack the union on the output side of the cell while it's operating and catch the drip in a cup and test to see if there's any FC there.

 

[JasonLion]

Phosphates never consume chlorine, that simply can't happen. Algae consumes chlorine, and if you have it you need to get rid of it. The first step to getting rid of algae is reliable test results.

After you add CYA it does take several days at least before you can get an accurate CYA test result.

Can you tell us a little more about what is going on? Is there any visible sign of algae? Have you done an overnight FC loss test to cheek for algae? What kind of test kit are you using, or are those results from a pool store?

 

[Phil3157]

I just put in 1# of HTH granular calcium hydrochlorite band will take a reading later and again in the morning to test for chlorine drop. Yes I am very tempted to take a water sample from the other end of the SWG cell tube but am reluctant to mess with it as cutting it will neccesitae a replacement plus all the re plumbing that goes with it.

 

[chem geek]

Your idea of adding another known chlorine source is a good one to see what happens. If it also ends up with zero FC, then I'd do a test for ammonia just in case the lack of chlorine after the refill and the addition of CYA had a conversion of some of it into ammonia by bacteria. Though that would also affect the bucket test, the bucket is so small that the SWG could have overcome the ammonia to eventually record a chlorine reading.

You really need to get yourself a good FAS-DPD chlorine test kit so you can distinctly measure Free Chlorine (FC) vs. Combined Chlorine (CC). As for ammonia test kits, you can get those at fish/pet/aquarium stores though with a FAS-DPD test and your adding chlorine to your pool you would be measuring some CC if you had ammonia in the pool.

 

[Phil3157]

Thank you all for your advice. 2 hours after adding the chlorine I came up with a reading of 3 on the drop test. This morning it is closer to 1, so I will definitely check out the ammonia possibility and post back which should be of benefit to others who may get the same issue. I think my problem is very rare though as I have researched it and did not come across the SWG issue.

 

[dmanb2b]

A 2 ppm drop overnight does not seem that rare All that indicates is that you need to complete the shocking process. Pleas use liquid chlorine as that will have the least amount of side effects. Granular chlorine adds either Calcium or CYA. To be able to shock, you will need to know your CYA level and have a good test kit on hand. Instructions are found here...good luck

pool-school/shocking_your_pool

 

[Ranger987]

I wasn't suggesting that phosphate remover kills algae, nor that phosphates consume chlorine. My personal experiences suggest that, in cases like the OP is experiencing, removing phosphates can help the issue - changing nothing else. I may not be using the your preferred terminology, but as algae is killed, phosphate levels can increase. Since phosphates are an algae nutrient, removing the phosphates can help prevent algae growth.

You state that algae consumes chlorine? Do you mean that it actually feeds on chlorine, or that the chlorine will be depleted as it kills the algae?

 

[chem geek]

You state that algae consumes chlorine? Do you mean that it actually feeds on chlorine, or that the chlorine will be depleted as it kills the algae?

The chlorine is depleted as it kills and oxidizes the algae.

The fact that phosphates are released when the algae gets oxidized isn't relevant because higher phosphate levels are food for algae that isn't able to survive and grow due to the chlorine that is killing it. Therefore phosphate removers should be seen in the same vein as algaecides -- they are an adjunct to slowing down algae growth, but are unnecessary if one uses sufficient chlorine to kill algae faster than it can grow.

 

[chem geek]

Thank you all for your advice. 2 hours after adding the chlorine I came up with a reading of 3 on the drop test. This morning it is closer to 1, so I will definitely check out the ammonia possibility and post back which should be of benefit to others who may get the same issue. I think my problem is very rare though as I have researched it and did not come across the SWG issue.

I don't think you've got ammonia in the pool, at least not anymore, since 1) it would consume the chlorine you would have added VERY quickly and gone to 0 ppm FC almost right away and 2) you are reading an FC that is dropping slowly in a way that is more consistent with killing off nascent algae growth rather than oxidizing ammonia or chloramines that only take hours to get rid of.

I think at this point, just focus on maintaining a shock FC level appropriate to your CYA level (as shown in the Chlorine / CYA chart) so that you completely kill off and oxidize all the algae. You will know that you are done when 1) the pool is clear, 2) the overnight FC drop is <= 1 ppm and 3) your CC is <= 0.5 ppm. At that point, your SWG should be able to keep up with the chlorine demand unless it is undersized for your pool in which case it may not keep up with the chlorine loss from sunlight during the day. I suspect it's OK for that, but is on the edge such that any nascent algae growth overwhelms it. You may also have had too low an FC/CYA ratio at some point allowing algae to grow faster than chlorine could kill it.