Algae and automatic pool covers

[Guest]

Hi

I am new here, but have spent a few days reading through a lot of post's about removing algae. I have had a continuous problem for several years - it the pump stops for a day due to a power failure or I forget to add a few lbs of Chlorine every day, back comes the green.

I understand now that what I considered to be "Shocking" the pool was inadequate and I need to go through a proper SLAMM process. However, part of this involves regular brushing to remove algae from the walls and steps etc. One post suggested that mechanical brushing is necessary as algae can form some kind of surface layer that makes it resistant to even shock levels of FC.

My problem is that I have a floating electrically operated pool cover, which is rolled up in a separate end chamber when the cover is open. Now while I can jet wash the top of the cover, I cannot clean the underside or all the gaps between the floating plastic slats. Then there is the problem with the end chamber and roll mechanism, which again is difficult to access unless I lower the water level in the pool and pump out the chamber. I am sure that there is algae lurking in the cover or chamber ready to burst back into life as soon as I stop cleaning and chlorinating for a day.

Is the SLAMM process likely to work my this case or do I have to drain the pool and replace the plastic cover slats to ensure that I really remove all the algae?

PJG

 

[chem geek]

Welcome to TFP!

Though you normally want to keep the pool uncovered during the SLAM process, in your case you could have the pool covered for at least a day or two to expose the underside of the cover to the high levels of chlorine. When the cover is opened, it will pull in the chlorinated water back into the chamber that should help keep the algae at bay. In fact, you probably have too low a Free Chlorine (FC) level for your Cyanuric Acid (CYA) level which is the root cause of the problem.

 

[Guest]

Thank you for your suggestions, although I new realise that the problem with the pool cover is rather irrelevant as I don't think I can do a SLAM anyway at the moment.

Over the last three seasons, in trying to battle the algae, I have put in a vast amount of chlorine - in the granule form of Dicloro 56%. As a result the CYA reading is off the scale. By diluting a sample of 1 part pool water with 3 parts distilled water, I get a reading of 110ppm which means that the true value of the pool water is 330ppm or 440ppm - I an not exactly sure if this a 3:1 or 4:1 dilution, but I think this hardly matters. The full readings are.

FC 0.52ppm
TC 0.74ppm
pH 7.0
ALK 133
CH 182
CYA 330-440

As I can tell see from other posts, the only thing I can now do is to drain the pool over the winter and then start again next year with new, clean water. It's not too bad, as I was considering draining the pool anyway as the paint is now blistering and flaking away from the mastic undercoat used to repair the underlying concrete walls - just a 3 year life. I seem to have made every mistake in the book - I wish I had found this site earlier!

PJG

 

[chem geek]

Well, that would certainly explain the situation. For every 10 ppm Free Chlorine (FC) added by Dichlor, it also increases Cyanuric Acid (CYA) by 9 ppm. Your pool's CYA is extraordinarily high and trying to kill off algae using chlorine would be nearly pointless. Water replacement is really your best option.

Using one part pool water with 3 parts distilled water is a 3:1 dilution, but you multiply the reading by 4 (for a 1:1 dilution you multiply the reading by 2). So you have roughly 440 ppm CYA.

 

[Guest]

Well, that would certainly explain the situation. For every 10 ppm Free Chlorine (FC) added by Dichlor, it also increases Cyanuric Acid (CYA) by 9 ppm. Your pool's CYA is extraordinarily high and trying to kill off algae using chlorine would be nearly pointless. Water replacement is really your best option.

Using one part pool water with 3 parts distilled water is a 3:1 dilution, but you multiply the reading by 4 (for a 1:1 dilution you multiply the reading by 2). So you have roughly 440 ppm CYA.

I am thinking of pumping this water into an underground tank that collects rainwater for irrigating our garden and vineyard. Would the high level of Cyanuric acid be harmful to plants? Should I just pump the lot down the drain - all 120m3 of it!

 

[chem geek]

The plants won't care and the soil bacteria would love the cynauric acid as a source of nitrogen and may even degrade it to ammonia which the plants would then use as a source of nitrogen. To be on the safe side, I'd water the area where you drain just to dilute it further.

If your chlorine level is high, you can dechlorinate or let the chlorine level drop before dumping the water. The plants won't like high levels of chlorine.

 

[Guest]

Thanks for the suggestion. There is no measurable chlorine in the water and it's nice to know that the cynauric acid may actually do some good. The pool water will actually be diluted with an equal amount of rain and well water over the winter before we start irrigating the lawns again next year so it should be fine.

PJG