Chemistry is good, algae still grows

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surfref32

Member
May 13, 2019
16
Pawleys island
Hello, I'm Andy from Pawleys Island, SC. We had our 17k gal gunite pool installed May 2011. I started reading this website and bought my first TF-100 right from the start. I've been able to keep my pool right with the knowledge I picked up here and the TF-100 until now. I have 2 issues really. The more important one is the algae. My goals are CYA @ 50 and FC @5 since the beginning and as long as I did that, all was well. I use HTH liquid chlorinator($4.99/gal @ ACE) and dry CYA when needed, usually only at the beginning of the season. My FC will normally drop 2 ppm in 24 hours in the Summer and I add the chlorine daily through a Pentair 300 feeder. I have a 1.5hp Jandy pump on a timer. I never close the pool or let it get green but when the water gets cold in Winter, I do let the FC drop to 0-2. A week ago I saw green algae growing in places on the sides and bottom. I was baffled because I've kept the FC steady @ 5ppm. I brushed the algae off, increased the pump on time to 6 hours a day and bumped up the FC. I've been running the pump 4 hours a day for years without issue. Today the algae returned so I did all the tests and I'm posting here. The secondary issue and one I've had for a few years is my PH requires acid often to keep in range. It will raise .4 in 3 to 5 days and faster when it rains. I'm out of patience, please help. Here are the numbers taken 15 minutes ago;

TF-100 renewed 4/3/20
FC:8
CC:0
ph:7.4
T/A:80
CH:250
CYA:55
Temp:82.6
 
Welcome (officially) to TFP! :wave: While you seemed to have a good thing going for about nine years, it looks like old-man algae finally caught up to you. You probably know that we always use the FC/CYA Levels to ensure our FC and CYA are balanced together. When the FC drops below that minimum FC level, which did happen in your case, the water is susceptible to algae. Not quite as fast in the winter, but it can happen. So if you see algae, you have no choice but to follow the SLAM Process. I'd round-up the CYA to 60 and increase the FC to "24" and maintain the SLAM level until you pass all 3 criteria.

As for the pH, hard to tell. Your pool is not new and the TA isn't high, but you can let it drop just a little more if you like (maybe 60). If you have aeration make sure those are off.
 
surfref32 said:
Are you saying that when I let the FC drop back in Jan and Feb the algae started then but wasn't visible until last week?
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The timeline is questionable, but it's a possibility. Even pools up north in much colder water turn green following the owner's best efforts, so it's certainly possible yours just happened to do the same even thought by your own experience and routine it never happened before. We never recommend allowing a pool's FC to fall to zero, so anything is possible. Once in the pool, algae can lay undetected in a hiding place for a long time and be present in various stages, so it's not always the obvious green water or algae plumes along the floor. A heavy organic load in the water can be virtually transparent and still clog-up filters. It's possible it started a few months back and between chilly water and your previous FC increases it wasn't able to get too aggressive. But if you're seeing it now, there's no doubt.
 
batesjer said:
Does the pool water get close to 60 degrees in the winter? That's about your average high temp in Jan and Feb right? Seems possible you could get slow growth during those months especially near the water line if your FC is 0.
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Honestly, I don't remember exactly how cold the water gets and of course it depends on the Winter we have. Last Winter was not particularly cold. I seem to recall water temps in the 50's several Winters ago when I did some polar plunging. :)


Bama Rambler said:
A couple things are confusing me. :scratch:

You said.


The 300 feeder is a tablet feeder. Are you using tablets in it every day? If so how are you maintaining the CYA
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I don't use tabs. I pour the liquid chlorine into the feeder daily. I use powdered CYA when needed.
 
surfref32 said:
Honestly, I don't remember exactly how cold the water gets and of course it depends on the Winter we have. Last Winter was not particularly cold. I seem to recall water temps in the 50's several Winters ago when I did some polar plunging. :)
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We always dose & maintain a min FC level for our pool's closing CYA whenever the temps get over 50/55 here. Never opened to a green pool :)

surfref32 said:
I don't use tabs. I pour the liquid chlorine into the feeder daily. I use powdered CYA when needed.
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Does your feeder go directly to pool returns or is it before the filter?
 
Please forgive me if this has been asked and answered a million times. I've searched and read for about 15 minutes but haven't found the answer. I know I need to SLAM the pool but we have family coming in tomorrow and I hate to close the pool to them if I don't have to. I've brushed it and I know we could use the pool until they leave and then SLAM it but I wanted to ask if there's another way to kill the algae and use the pool at the same time? Thanks! Andy
 

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It is safe to swim up to slam level. Check your CYA again just to ensure you have an accurate test as the slam level depends on it.
 
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