Total dissolved solids causing problems?

[JohnRoss]

The last two years we have had the dreaded green pool problem. Before that only the odd trace of green which was easily removed. The question is does this information provided by a certain web site hold true. The total dissolved solids (TDS) builds up over several years. When these get too high, chemicals may become "locked" and unable to work properly. The result is water becomes unhealthy and algae may form. When this happens there is no other option but empty and replace the water.

Last year I was able to clear the green by pouring in Javel once, about 10 litres of 9.6%. This year it was again very green and it took 15 litres of Javel a few weeks ago to return it back to a nice clear sparkling pool. In the past chlorine tablets have only been added at the beginning of the season to give it a bit of a choc and it has stayed pretty clean for the rest of the year. The pool is a Desjoyaux salt water pool with chlorine produced by an electrolytic cell and contains about 75 cubic metres of water. I would like to solve the problem without replacing the water bearing in mind possible restrictions on water usage. The problem being that almost overnight it has gone green again. Could this be due to the accumulation of disolved solids and how many times can you pour Javel into a pool? The chlorine reading took a long time to drop back to a safe level last time I poured in Javel earlier this year. The current ph and chlorine level is about right but needs must or does it? I have run the pump and changed and cleaned the filter bag on a daily basis for the last few weeks but despite this the dreaded green is back! So any suggestions folks?..........................JR

[Théière]

Hi JohnRoss,

I will try to leave out my previous poor water circulation comments and move on but that with Desy pools is always at the fore front of my mind.  TDS, in a salt pool is always very high because you have salt in it so it doesn't really make a jot of difference unless some of the TDS is something you don't want.  I don't know if you can test for cyanuric acid or how you are testing but cyanuric acid (CYA) build up is a problem over time.  That is one test you really do need and not via dip strips which are all but hopeless for CYA testing.  There are other areas such as high phosphate and or nitrates which affect the algae growth rate as they are both primary sources of food for algae.  It has however been proven that if the chlorine level is kept up and not allowed to drop then this area can almost be forgotten about, although personally I prefer to lower phosphates to lessen any chances of algae getting a foot hold.

If you carry out the overnight chlorine test, this would indicate what use of chlorine you have and the general state of the water for life support.  The problem is you need accurate testing to carry this out.

In short posting a full set of test results will help including water hardness, total alkalinity, pH, Chlorine level (free and total) and CYA level.

It's not beyond the realms that your chlorine generator and or cell is coming to the end of it's life and not producing enough.

You can continue and should continue to use javel as often as you like/need, you are dabbling with chocing the pool but really need to fully choc treat the pool and that doesn't mean using choc, javel is quicker acting and contains no CYA so won't raise the level. Brushing the sides is important too but maintaining the correct choc level of chlorine for as long as it takes and not just a one or two shot treatment.  The javel 15 litres should have raised the free chlorine level to around 20ppm but that would have dropped back quickly and unless the regular additions were made then any living algae would again multiply.

Test results should be the next step.

[JohnRoss]

Hi and thanks for coming back on this. Tested the pool this morning and the thingy which uses Phenol and DPD tablets read 7.5 for pH and 3 mg/l for chlorine. The electrolyic cell is running at 10 amps which is what it normally is. I will add some more Javel and see what happens. Cannot measure anything else as have not got any other kit. Pool temperature 20 degrees and rising. Salt was added as usual at the begining of the season to compensate for loss due to pumping out surplus water caused by Winter rain and  to give the cell current of 10 amps. Robot has been in the pool several times and no visible debris now plus have brushed the sides and no green accumulations just a uniform green colour to the pool water. Changing and washing the filter bags daily alternating 6 and 15 microns. Anything else I should do?.........JR

[Théière]

Send me a water sample to test for you?

Raise the free chlorine level to nearer 10ppm and try to hold it there, the clear green tinted water should go blue/grey and a bit cloudy when you are killing the algae otherwise you are probably not getting on top of it.

What do you use to wash the filters, washing powder/liquids are loaded with phosphates to make them generally more effective and surfactants lower the surface tension of the water so smaller particles can pass through the filters unchecked

[JohnRoss]

Thanks for the offer and I will get back to you about that if I cannot clear it. I was in trouble for putting the filter bags in the washing machine, did not use soap powder, as it left a lot of muck muck in the machine and 'er indoors was not happy. In fact the washing machine did not shift much of the embedded muck so I reverted to blasting the bag all the way round from the outside with a high pressure water jet from the garden hose and that has always worked quite well. I have put some more Javel in the pool so waiting to see what effect that will have. The testing kit does not read higher than 5 but last time when I put 15 litres in it went very red and must have been well over 5. One bag is a bit the worse for wear so I will be replacing it. Has lasted over 10 years so not too bad...........Your help is appreciated............JR

[Théière]

JohnRoss, I suggest you stick to 7.5litres at a time as that should get it to around 10ppm.

If you dilute a sample of pool water with the same amount of tap water, then measure that in the usual way but multiply the result by 2 that should give you an indication of the level of chlorine over 5ppm. do this quite quickly as it can bleach out the sample.

[JohnRoss]

Will do and a brilliant idea. I will try that this pm and try to keep it at 10. I cannot remember how long it took for the green to go last time but I guess it is not instant, thanks.................JR

[JohnRoss]

Ok tried it this pm and it is now reading 10 or there abouts so will monitor over the next few days and it may be my imagination but the green does not look so strong. One thing that does occur to me is that we have had the Summer cover off for the last few weeks as it is falling apart and we intend to shortly replace it. In the past I have noticed that the only place we tended to get algae was at one end where the cover did not quite reach and the light got in. The cover was only wound off when we used the pool whereas now it is uncovered all the time. Could this make matters worse I wonder?........JR

[Théière]

Yes to a degree, it depends on the colour of the bubble cover, dark blue types keep out the sun to a greater degree than clear covers so slowing algae growth down. Being darker they also don't warm the water as much as a clear cover. It's a trade off but keeping the chlorine level up is the best cure.  With the pool properly choc'd and the chlorine at the correct level algae without a cover should not be an issue.

If you are considering a new cover, one of the latest designs makes real sense The Geobubble