UV/Peroxide Conversion

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Pwareing

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May 4, 2018
65
Carcassonne France
Hi all, normally not one to panic too much but end of season and time to change from crazy expensive UV/Peroxide system to UV/Bleach (or even just Bleach) system and it didnt go exactly how I imagined. Left the Peroxide to run out and then converted to Bleach with auto dispenser. Next morning all blue and clear but no chlorine reading so added a 20litre drum of 10%. 1 hour later pool was green then another hour went by and pool was brown. Can still see leaves on the bottom of the deep end but definate brown. Have added another 20 litre of 10% but had to leave site with chlorine level around 5ppm.
My question is do I just need to keep adding Bleach as I would normally do to overcome a green pool or is this some other kind of problem? Should I turn off the UV?
Only have access to test strips for Peroxide and Aquacheck tru test for the chlorine here in France - Taylor not available.
Thanks for any help or advice
 
The color change when adding chlorine indicates iron. Not sure about the filter -- have not heard of that one. It sounds like iron, which can stain the pool surface.
 
The pool was always showing vivid bright green algae in the circulation deadspots but water was clear. I cleaned the pool 3 times per week so it never got to build up. All went well all season and I had put off the changeover until the season was over. The chlorine level was zero at 10h00 so I added the Bleach. Even then the level dropped from around quickly to 5ppm so I just thought it was expiring due to killing the green stuff? Is there a simple way to test for Iron or remove it - its a liner pool.
 
Pwareing said:
Would the volcanic ash filter do anything weird? Expected it to be inert.
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Depending on the source location of the ash material, it can contain iron-bearing minerals that are leachable. There is nothing wrong with standard pool filter sand and I would suggest you convert your sand filter from volcanic ash to standard pool sand.

Clean and sanitary swimming pools will never have visible patches of algae. If you were seeing that in your pool then the sanitizer was not doing it’s job. Peroxide is an ineffective sanitizer at levels considered safe to swim in. UV light will only affect planktonic algae and bacteria. So, as you are aware, converting to chlorine and performing a SLAM will solve your algae problem.

As for the iron, there’s no telling how much is in your water. You can try to filter it out using poly fill but expect that to take a long time. You can try using a sequestering agent but that requires very careful control of the water chemistry to keep the iron in solution. And it gets expensive.

Municipal water supplies can still have appreciable amounts of iron in them because it’s not considered an actionable contaminant by most regulatory authorities. So you’ll need to figure out what sources of iron you have to know of draining your pool and refilling will help.
 

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JoyfulNoise said:
Depending on the source location of the ash material, it can contain iron-bearing minerals that are leachable. There is nothing wrong with standard pool filter sand and I would suggest you convert your sand filter from volcanic ash to standard pool sand.

Clean and sanitary swimming pools will never have visible patches of algae. If you were seeing that in your pool then the sanitizer was not doing it’s job. Peroxide is an ineffective sanitizer at levels considered safe to swim in. UV light will only affect planktonic algae and bacteria. So, as you are aware, converting to chlorine and performing a SLAM will solve your algae problem.

As for the iron, there’s no telling how much is in your water. You can try to filter it out using poly fill but expect that to take a long time. You can try using a sequestering agent but that requires very careful control of the water chemistry to keep the iron in solution. And it gets expensive.

Municipal water supplies can still have appreciable amounts of iron in them because it’s not considered an actionable contaminant by most regulatory authorities. So you’ll need to figure out what sources of iron you have to know of draining your pool and refilling will help.
Click to expand...
This sounds like a nightmare? If I drain a refill how do I know water has no iron - will it do the same again?? How do I filter - in skimmers? Would the chlorine level still drop if it was Iron? Would the colour brown increase the more Chlorine I add? - sorry for all the questions. Peter
 
Eventual success
Ok thank you for all your inputs. The pool is virtually back to crystal clear blue but it just goes to show how much algae can be in a crystal clear blue UV Peroxide pool.
Yes there were the small green areas in bad circulation corners that I was brushing 3 times a week but nobody spotted/registered this or complained.
I was told this was normal by the previous pool professional/pool builder/pool store owner who considered himself an expert.
It took just over 100 litres of 10% bleach to clear it to where I am now!!!
An absolute garbage system which was VERY expensive to install and VERY expensive to run and maintain.
The brown colouration worried me because no other pools have behaved that way - perhaps due to peroxide or the type of algae? It was very bright vivid green.
Thanks again
Peter
 
Great things are working out. Your description originally with brown water after adding chlorine is a classic sign of iron.
 
Have you backwashed the filter yet? If so, give it a good backwash and rinse and watch the backwash water discharge to see what color it is. You filter may have captured a good deal of debris including any precipitated iron (rust) if the particulate size is big enough.
 
Yes I backwashed and rinsed and a little bit more bright green was pumped back into pool when I returned to filtration.
I was talking whilst the backwash took place so missed the initial time section of the backewash/sight glass so cannot say for sure if iron has been filtered out?
The filter material was "Zeolite" if I recall correcty.
Thank you once again.
Peter
 
Just to add a thought - I read that Zeolite can be used to remove iron from water - so are we saying the iron could have built up in the Zeolite then converted by the chlorine when I raised the chlorine level which sent the water brown colour?
The brown disappeared virtually overnight (no pillow stuffing or extra filter material apart from skimmer nets) leaving slight green and another 24 hours its clear. All very confusing I thought is was going to take ages, maybe Zeolite is a very good filter material?
 
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