Black pool algae & cal on pool floor

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fearless nige
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Black pool algae & cal on pool floor

Postby fearless nige » Sun Aug 12, 2012 2:41 pm

Two different problems in two different pools. Can anybody shed any light?

A neighbours pool has some nasty black algae on the side walls of their pool - no amount of scrubbing appears to dislodge it and a high chlorine level has no effect. I also bought some rediculously expensive 'Algae Killer' - a dark blue liquid. Nothing has worked. Any ideas? The sand was changed end of last summer. Levels appear correct (Ph etc).

Another neighbour has a nasty sandlike cal deposit on the floor of the pool. Is it cal? Any ideas how it can be removed? It appears to be quite solid!! The pool was completely emptied prior to being filled a short time ago.

Thanks, and help!!!

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White Horse
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Re: Black pool algae & cal on pool floor

Postby White Horse » Sun Aug 12, 2012 3:01 pm

I've had experience of both of these problems.
Black algae is a pig to get rid of, but it can be done. Black algae forms a crust over itself which has to be scratched open. You will need to brush it vigorously with a nylon brush, or LIGHTLY with a stainless steel brush. Now increase the chlorine in the pool to 20 ppm and keep it there for 3 days. During day 2-3 you should be able to brush the algae again to keep the capsules open.
It is the encapsulation that makes it so resilient. To get a pool up to 20ppm takes a shock dose of 20 grams per cubic meter, so you will need 1.5kg in a 10x5 pool or about 1kg in an 8x4 pool.

Cal on the floor - brown cal is a mixture of impurities and calcium carbonate and the way to remove it is not by brushing. It has to be dissolved by decreasing the pool pH. Test the pool pH and I feel sure it will be high (alkaline) and you need to add acid until the pH is 6.8. (Very weakly acidic) Keep it at 6.8 until the deposit has dissolved. It might take a week or so. It will soften up and brushing with a nylon brush will then help.

Keep at it. The pool with black algae will be susceptible to regrowth as it hides in the grout, so never let the chlorine level drop below 2ppm.

I hope this helps, let me know how you get on.

fearless nige
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Re: Black pool algae & cal on pool floor

Postby fearless nige » Sun Aug 12, 2012 6:06 pm

Thanks a million. I will try that.

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Re: Black pool algae & cal on pool floor

Postby Chunky Monky » Sun Aug 12, 2012 11:32 pm

Hi WH - probably a stupid question, when the chlorine is up to 20 ppm is the pool out of bounds for swimming etc?

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White Horse
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Re: Black pool algae & cal on pool floor

Postby White Horse » Sun Aug 12, 2012 11:34 pm

Chunky Monky wrote:Hi WH - probably a stupid question, when the chlorine is up to 20 ppm is the pool out of bounds for swimming etc?

yes

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Martin Page
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Re: Black pool algae & cal on pool floor

Postby Martin Page » Mon Aug 13, 2012 8:27 am

The black Algae is the harbinger of a pool re-grout.
A couple of years back I tried to fight black Algae for a whole season with little or no effect no matter what the treatment. Then over the back end of the year we drained the pool and re-grouted it.
When you looked closely at the grout it was nearly 3 cm below the height of the tiles so there waas now way the pool vacuum could get in to dislodge it
We scraped out the remaining grout . Flushed withe neat bleach and alowed it to dry, and re-grouted with a hydrophobic pool grout ( waterproof quality compared to standard grout but by the same company)
Since then ... Touch wood ... no Black Algae

fearless nige
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Re: Black pool algae & cal on pool floor

Postby fearless nige » Mon Aug 13, 2012 8:47 am

Ouch - that's a big job. Thank you for your input. I am beginning to think a serious overhaul of the pool may be necessary.


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