High Alkalinity/PH Plus black algae

Keith1994 · Postby **Keith1994** » Mon 30 Aug, 2010 15:34

I'm helping a friend take care of a pool that has been giving her fits. She's got some spots of black algae that simply are not affected by shock or algacide. Her alkalinity was at 260 and the Ph was 7.8 to 8. I've been trying to lower the alkalinity and the Ph by using muratic acid. Neither have dropped much over the past 3 weeks. I've attempted to do it by adding a little at a time every 2-3 days. The pool does not hold chlorine well and needs to be shocked every 4 days or so even when the chlorinator is set on 5. The pool is older and it may need to be replastered. If so, does that somehow effect the effectiveness of the chemicals? Could that be why the algae will not completely go away? In all likelyhood the filter needs new sand too. I feel overwhelmed and I'm not sure what to do. A pool professional was handling the pool before I started and he was dismissed because the pook continued to go green. I'm at a loss. Please help!!!

Postby **chem geek** » Mon 30 Aug, 2010 15:50

Get a good test kit such as the Taylor K-2006 or TF-100 to determine your Free Chlorine (FC), Combined Chlorine (CC), Total Alkalinity (TA), Calcium Hardness (CH) and Cyanuric Acid (CYA) levels. The CYA level in particular may be very high in this pool due to continued use of stabilized chlorine products and that makes any chlorine you add much less effective. Read the Pool School for more info including the article on Defeating Algae. Note that you may need to do a partial drain/refill to lower the CYA level if it's high.

James Watson · Postby **James Watson** » Mon 30 Aug, 2010 16:01

If the plaster is rough, then black algae will get deep into the plaster and is difficult to remove. In addition to getting your chemistry right, you need to use a stainless steel brush and brush the algae very vigorously and frequently.

Keith1994 · Postby **Keith1994** » Fri 10 Sep, 2010 14:22

Thanks for the suggestions. I initially scrubbed the pool with a wire brush and still could not get it all. I really think this is a case where the pool will need to be drained.

swimfit · Postby **swimfit** » Thu 24 Feb, 2011 06:00

You are right. If the suggested hasn't worked for you, and that which involves rigorous scrubbing, you perhaps will have to give it a treatment draining off the water. How long has it been since the problem occurred?