Green algae problem but chlorine ok?

[arakasi55]

Hi everyone, I seem to have an ongoing issue with green algae in my concrete tiled pool. This started earlier this year around March and has been ongoing.
I have SLAM'd the pool twice, allowing not just 1 night with zero loss but at least 3. Both times I never had any CC readings. The second time I did this (start of November) I pulled my cleaner, hose, pool lights all out of the pool, submerged them in a chlorine solution and scrubbed to ensure all algae was removed.

I don't use any additional chemicals in the pool like algaecides and have been intentionally leaving my FC levels higher than my usual 5.0ppm to try and combat the problem. Before I resort to going to the dreaded pool shop and get told to simply add algaecide, I was hoping for some suggestions as to what to check/try as I'm struggling to understand what could be causing this.
While there are some trees around the pool, I'm pretty diligent in cleaning out whatever my suction pool cleaner doesn't and brush the walls every 1-2 weeks (ok, prolly more like every 2 weeks )

My pool specs are ~50,000 litre, glass tile over concrete, sand filter with glass media and SWG.
I use a Taylor K2006 test kit and recently replaced all the reagents.
My last two tests are as follows:

6/12
FC - 6.5
CC - 0
PH - 7.4
TA - 70
CH - 350
CYA - 55
Salt - 4000

28/11
FC - 7.0
CC - 0
PH - 7.6
TA - 70
CH - 350
CYA - 55
Salt - 4000

Thanks a lot in advance!

 

[arakasi55]

Here are some images of the problem. Note that while it seems most prevalent on the steps and in corners, it's also on the walls near the coping

 

[kimkats]

Does it "poof" when you wave your hand in the water?
Have you taken the lights out and scrubbed behind them?
Do you cover the pool with any kind of cover?
Did you take a toothbrush and scrub all around the returns and skimmer?
Did you brush the pool during the SLAMs?
Did you leave the pump on 24/7 during the SLAMs?

How are you testing the water? (please put this info in your signature)

Have you looked at the glass media in the filter?

Sorry for the many questions but your pool is showing the SLAM is not done. Trying to find what is causing this to happen.

 

[Newdude]

Is it only a visible problem or are you seeing a FC loss also ? Your Astral SWG and use of liters tips me off that your season is probably winding up as ours winds down.

So if you aren’t seeing an unexpected daily loss, or failing an Overnight Chlorine Loss Test, it could just be your pollen season. Pollen collects in the lesser circulated areas like steps and corners, exactly like yours is showing, but typically doesn’t affect the chemistry by much. It’s also usually coated on everything like the deck and cars.

 

[JohnT]

Any possibility it is pollen? Maybe wipe a damp white cloth on some horizontal surfaces near the pool to see if there is a yellow dust on them.

 

[kimkats]

OH GOOD CALL guys!!!

 

[arakasi55]

Thanks for all your replies so far, I'll try to address them all

• Does it "poof" when you wave your hand in the water? Good question. It certainly does when I brush it, will test if it does it by hand.
• Have you taken the lights out and scrubbed behind them? yes, scrubbed and submerged in a high level chlorine bath for around 24 hours.
• Do you cover the pool with any kind of cover? yes, there is a cover that usually goes on in summer, but off in winter. Having the cover on or off doesn't seem to affect the issue.
• Did you take a toothbrush and scrub all around the returns and skimmer? yes, with a small scrubbing brush
• Did you brush the pool during the SLAMs? yes twice per day
• Did you leave the pump on 24/7 during the SLAMs? yes pump was on 24/7
• How are you testing the water? (please put this info in your signature) Taylor K2006 kit with recently replaced reagents as noted in my OP (will add to sig)
• Have you looked at the glass media in the filter? this I haven't done. It was replaced around 4 years ago and is backwashed every fortnight. The viewing glass is clear following backwashing
• Is it only a visible problem or are you seeing a FC loss also ? Your Astral SWG and use of liters tips me off that your season is probably winding up as ours winds down. I am not seeing unexpected any FC loss and CC continues to be at 0. I am in Australia, so yes, it's early summer here. I will perform another OCLT tonight and report back
• Any possibility it is pollen? Maybe wipe a damp white cloth on some horizontal surfaces near the pool to see if there is a yellow dust on them. I will try this test and report back, however it is sitting on vertical faces of the pool as well as the pool having it's cover between the last test I did on 11/28 and when I took it off for some warmer weather three days ago

Thanks again for the help!

 

[kimkats]

What a puzzle! Do you have a turkey baster? If so use it to see if you can suck up any of the stuff. Put a white paper towel in a strainer and squirt the water in the baster out. Let the towel dry out and let us know what it looks like once it is dry.

 

[arakasi55]

That sounds like a fun experiment! I'll give it a shot and report back along with the OCLT results.
Thanks for the suggestion

 

[aussieta]

is this on the north walls of the pool
as has probably been well shaded for last few months
looking at your pics it is shaded
my pool also gets a green haze on the north vertical surface during winter .when i dont brush as often

 

[arakasi55]

Hi, the steps indeed are at the northern end of the pool and it's fair to say it's the northern end that seems to cop the worst of it, while the eastern side (which gets afternoon sun) tends to fare better.
We've had the pool for around 12 years now and it was originally rendered. We stripped this back around 5 years ago and tiled the pool and have never had this issue until this year (first noticed in May). The water chemistry is much stabler now than it has ever been, but by the same token, the plants have all matured in that time so are likely shading the area more.

 

[Newdude]

. I am not seeing unexpected any FC loss and CC continues to be at 0. I am in Australia, so yes, it's early summer here. I will perform another OCLT tonight and report back

Awesome !!! So going forward, anytime you question anything about your chemistry, you don’t even need us. Perform an OCLT which takes the sun and the regular daily FC loss out of the equation. If you lose more than 1 FV overnight with no UV or swimmers, it’s an organic problem like algae. If the FC holds, not only do we know it’s something like pollen, but you are no longer worried about losing ground to a algae bloom if it takes a bit to figure out the rest. Still ask away here if you’d like, it keeps us busy and we like to help.

I had crazy pollen / debris both early and late season and would go cloudy for a few weeks. The first few years I took many trips to the pool store before I just knew what I was looking at and how to prove it. If it does turn out to be pollen, only time and filtering will help. And you’ll be brushing / vac-ing in the meantime until it’s done.

 

[Newdude]

For reference this was my filters after a SLAM
This was them after 3 or so weeks of pollen. It *can* be some nasty stuff,

 

[arakasi55]

Wow! that's crazy!
The OCLT was 0.5 loss. 5.5ppm tested last night and 5.0 this morning.
I also attempted using a baster to suck up some of the offending stuff, although as I only scrubbed on Monday evening there wasn't much to gain and there was literally nothing on the paper this morning. I'll attempt this again.

For reference, here is a closer shot. Note the dark spots under the tiles are just the glue backing as they are very light glass tiles.