Ongoing Nuisance Algae Problem

socalsharky

Bronze Supporter
Apr 27, 2009
42
I have had an ongoing algae problem that I can't solve. The first place it shows up is on the pool steps and on the plastic parts of the pool vac. I have a SWG and never let the FC drop below 5 ppm. When it first shows up it is relatively minor and I just deal with it by brushing and occasionally elevating the FC to 20 ppm. Anytime the algae gets bad, I SLAM the pool, pass the overnight test, and all is good for a month or so, and then the algae comes back. When it shows up it is relatively minor and I just deal with it by brushing and occasionally elevating the FC to 20 ppm. This has been going on for a year or two. I brush the pool once a week. Not sure what I am doing wrong, but I'm pretty sure I should have to be SLAMming the pool once a month to keep the algae at bay. I only did a limited brushing last weekend, so it was particularly bad this morning. Here is the water chemistry:

FC: 11 ppm
CYA: 70 ppm
TA: 70ppm
pH: 7.4
Salt: 3400 ppm

I am stunned that the algae can grow in these types of conditions, with a water temp around 60 degrees. Could it be phosphates?
 
Last edited:

socalsharky

Bronze Supporter
Apr 27, 2009
42
What is your cya level?

Phosphates don’t matter if you have proper FC level for your cya per chart.

Apparently you have some hidden spots, niches, ladder etc that are not completely algae free.
Sorry, meant to say CYA, and not CA.
CYA is 70 ppm. I corrected my original post.

Perhaps there are some areas of the pool that are not completely free of algae after the SLAM. However, I previously have kept the chlorine at SLAM levels for nearly a week, and have passed the overnight test. The algae always comes back. What else can I do to eliminate these hidden spots?
 

Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
11,511
NY
What else can I do to eliminate these hidden spots?
Find the source. Ladder/ hand rails hold several gallons each, light niches, all up in the skimmers, auto fills, stair trim, etc. it’s hiding in plain sight and being reintroduced somewhere. Every last inch is suspect until you prove it otherwise.

if you’ve scoured literally every inch, deep clean the cartridges. It’s nice when you just stay clean and don’t have to do the cartridges, but really, they should be done either way just to be sure.
 
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Auburn02

Well-known member
Oct 8, 2019
271
Mobile, AL
I'm very early in my pool ownership (less than a year) but like you I've never had my FC drop below recommended levels and usually am quite close or just over the upper end for my given CYA level. Yet like you, I have had a fine green film show up 2 or 3 times. Typically I can't even tell it's there until I brush and see the slight green "poof" off the brush. The suggestions here are all worth investigating; in my case I have no ladders (vinyl covered steps only), no hand rails, no light niches (microbrites instead), etc. Very perplexing. I do leave my robot in the pool for days on end, but being submerged in the adequate FC I'm not sure why/how that could be the case but suppose it's a possibility.
 

socalsharky

Bronze Supporter
Apr 27, 2009
42
I'm very early in my pool ownership (less than a year) but like you I've never had my FC drop below recommended levels and usually am quite close or just over the upper end for my given CYA level. Yet like you, I have had a fine green film show up 2 or 3 times. Typically I can't even tell it's there until I brush and see the slight green "poof" off the brush. The suggestions here are all worth investigating; in my case I have no ladders (vinyl covered steps only), no hand rails, no light niches (microbrites instead), etc. Very perplexing. I do leave my robot in the pool for days on end, but being submerged in the adequate FC I'm not sure why/how that could be the case but suppose it's a possibility.
Glad to know I'm not alone :LOL:. I didn't really have this problem in the first couple of years that I owned the pool, which leads me to believe that something like phosphates is contributing to (not causing) the problem. Like you, no ladders or other places that algae could hide.
 

Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
11,511
NY
which leads me to believe that something like phosphates is contributing to (not causing) the problem
It totally is a thing. It’s an irrelevant thing for 99% (?) of pools, but with 10M+ pools in the US, that’s still 100k that matter. So statistically speaking it’s not your issue and we cannot advise it to the masses. Especially to the newbs coming in grasping at straws and looking to validate the bad pool store advice they’ve gotten. But once you’ve thoroughly checked off everything else, it’s worth exploring.
 
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borjis

LifeTime Supporter
Aug 19, 2014
3,507
Pacific NW
Phosphates are food for algae.
A buffet is an example. The food is there...yes. but if the doors to the buffet are locked (by chlorine) then the organism can't feed as the chlorine keeps it from existing.

Somehow the algae is not being fully killed off.
Maybe try finishing the next slam at mustard algae levels.
 

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pb4uswim

Well-known member
Jul 23, 2020
331
Michigan
A little late, but just wanted to weigh in and let you know you’re not alone. I just closed my pool for the season, but I had a very similar experience. My pool is fiberglass so there really just is not many places for the algae to hide, but there it is, every so often throughout the season. I’m struck by your comment “I am stunned that the algae can grow in these types of conditions”, as that is exactly how I felt.

Of course this won’t help, but because of a crack found in my pool, I have to drain the pool next year. You can bet I’ll be checking out every nook or cranny while the pool is dry. I’ve even thought about taking a garden type sprayer and coating the pool with a strong mixture of chlorine and water. We’ll see if they let me anywhere near the pool while the repair goes on.

One thing I noticed in this thread is the recommended to clean your filter. I always assumed that with the SLAM level water going through it, the filter could not be the problem. However, maybe I’ll start cleaning my filters more frequently and deep clean them instead of just spraying them off.

Good luck.
 
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