Algae under plaster

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FormerMurkyLagoon

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Apr 24, 2016
7
Tampa Bay Area, Florida
Hello,

Love the site. You guys have been such a big help in getting my pool straightened out. I'm coming up to speed on testing at home and keeping the chlorine levels stable. First post. My pool is clear right now.

FC 2
CC 0
pH 8.2
CYA 45
CH 150
TA 90

Background: House was a short sale and the pool was black for about a decade before I bought it. The plaster surface is in really bad shape and de-laminating in many places. Calling the plaster soft would be an understatement. Staining is rampant. It will be two years before I can re-plaster the pool after the interior remodel is complete.

Question: There is a thriving population of green algae growing UNDER the plaster that invariably starts peeking out around the delaminated areas even with FC at 2. I'm struggling to keep things in check without reverting to algaecide. Considering my test results, would SLAMing be effective in my situation? What chlorine level should I maintain after I SLAM? 3ppm? 4 ppm? Any other advice on how to best ride this out for the next couple years?

Many thanks in advance for your advice.
 
Last edited:
Hello and welcome to TFP! :wave: To effectively perform a SLAM and kill algae, your FC must be high enough to meet your current CYA as noted on the Chlorine/CYA Chart (link below). That is very important. Your FC right now is very low and not even close to SLAM level. Good thing is you already have a TF-100. :goodjob: So first, lower pH to 7.2-7.5, then increase FC to "20" which matches the corresponding CYA of 50 requirement. Follow everything you see listed on the SLAM page (link below) and you should definitely see improvement..... at least in the elimination of algae.

Also, you should consider increasing CH right away. Too low causes the plaster to erode which may be part of the problem in FL due to all the water exchange from rain. Minimum level for your pool is 250 ppm.

Hope that helps.
 
Hello, Texas Splash. Many thanks for the advice. The FC levels I'm maintaining right now are just normal levels, at least that's what I understand from you guys. So since I have persistent algae even though the pool is clear, your response seems to indicate a SLAM would be beneficial for my situation, correct?

Since the plaster is in such sad shape, is it worth the expense to raise the CH? Will low CH cause other problems?
 
Yes, the SLAM is the only way to get rid of the algae. Increasing and maintain the CH won't help any previous damage, but it might help slow-down any future erosion. Right now you're just trying to buy some time, so anything you can do chemically will certainly help. It's not much money to buy some calcium chloride or calcium chloride dehydrate. I would raise it to at least 250 if I were you. Your recommended max is 350 ppm, so you could go even higher.
 
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