Yellow algae won't go away!

Macysumo

Silver Supporter
Jun 27, 2020
37
Pensacola Florida
New user, took over pool maintenance when COVID-19 came and pool guy quit. Have read ABC's and understand SLAM process but I must be missing something...My yellow algae keeps coming back.

Big problem was CYA. Started at 110 and after much work I've gotten it to 70 so I've put in gallons and gallons of Liquid 11% Chlorine but unless I add Calcium Hypochlorite the yellow algae just hangs around...keeps coming back after a couple of days.

Two days ago I used 4 lbs of Calc Hypo (while CYA 100) and after I got algae death I vacuumed to waste, backwashed twice and refilled my pool 7 hours with garden hose. Yesterday clear water, CYA 70, pH 7.2 and a half gallon of Liquid Chlorine.
Today CYA 70, pH 7.2 TA 100, FC 39ppm and algae is back. I added another two gallons of Chlorine.

Chlorine/CYA says 70CYA is 28ppm SLAM and 40.5 for yellow mustard SLAM. What am I missing?
 

YippeeSkippy

Mod Squad
LifeTime Supporter
Jan 17, 2012
14,815
Evans, Georgia
Hi there Macysumo :)

Are you brushing daily? Unless your chlorine is older, weaker for some reason I can see no reason why CalHypo would work better for you?? Is the algae in only a particular spot repeatedly?

How are you testing your water?? Which kit?? How high is your CH? How do you normally chlorinate your pool?

Please fill out a signature with details on the pool size, surface type, equipment used, test kit, etc. You can find it under "Settings"

Maddie :flower:
 

Macysumo

Silver Supporter
Jun 27, 2020
37
Pensacola Florida
Yes, brushing daily. Chlorine is new (got 5 Gal. at local ACE Sunday). Testing was with Pentair kit... no Chlorine except Residual which gave me no info but TA and pH so I "estimated" how much Chlorine to use.
Now have TF-100 and am at Yellow SLAM level but it appears. Started with little tiny dots then blooms into splotches.

Didn't do CH as I have vinyl pool. Is it needed? Water is clear.

I do have TriChlor in tablet dispenser but it's turned off. I just pour liquid Chlorine into pool near skimmer to Chlorinate. Signature should be active now.
 
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Macysumo

Silver Supporter
Jun 27, 2020
37
Pensacola Florida
FYI, I used pool math to “estimate“ chlorine amount before I got TF-100.

Algae is pretty much in same places (three corners and a bit down the sides) but not exactly... develops differently from time to time.
 

mgtfp

Bronze Supporter
Mar 5, 2020
473
Melbourne, Australia
The trick with yellow algae is that you first have to complete a normal slam, i.e. maintain slam level until you pass all 3 criteria. Then you raise FC to mustard algae slam FC for 24 hours.

Some users report that after that they need to maintain an FC level that is above the standard target range for a while. Mustard algae can be very persistent.
 

Macysumo

Silver Supporter
Jun 27, 2020
37
Pensacola Florida
Thanks! Like the forums here!

I will say that with the exception of today‘s appearance, each mustard algae instance has come after a heavy rain storm. We live 400 yards from the intercoastal waterway so we could be getting some from there.

Will keep after it. My LED light niche has some “dirt“ or dust coming out when I brush it. I thought it was rust on a screw but maybe there is a colony behind that...
 

mgtfp

Bronze Supporter
Mar 5, 2020
473
Melbourne, Australia
How does your water look like, and do you have an increased chlorine consumption?

And remember that the mustard SLAM level is designed for a 24h period, not for longer periods.

I'd suggest to bet back down to the standard SLAM level for now and run an Overnight Chlorine Loss Test

Then we'll know what we are dealing with and can take it from there.

If you have recurring yellow algae as you described, then you might want to consider a higher FC-level in normal operation. In the original CYA/FC-table by Chem Geek that is the basis for the current table, there is an additional column " Yel/Mstrd Min". Some users with recurring mustard algae problems have reported that sticking to this FC-level in normal operation helped them to prevent further outbreaks:


But first we have to get the current outbreak under control.
 

Macysumo

Silver Supporter
Jun 27, 2020
37
Pensacola Florida
Water looks pristine...super clear.
Yes, that original CYA/FC chart is the one I've been referencing.

This morning quite a bit of the algae had disappeared from the bottom but there are three areas that have persisted. One spot about 3x3 inches, a small sliver 1/2 in. x 3 in. and in some grooves in the stairs that gets very little flow from the pump.

By noon it was all gone except around the stairs and I swept that to get it into the main pool hoping the chlorine in there will kill it. I had added another gallon of 11% Chlorine before I went to bed so it took roughly 12-14 hours at that high level (probably around 50ppm) to kill those spots.

I tested Chlorine at noon at got FC 28.5 and CC 2 for TC 30.5 PPM.

There were NO remnants on the bottom...is that normal?
 

Macysumo

Silver Supporter
Jun 27, 2020
37
Pensacola Florida
One thing that bugs me is the CYA testing. I have the Pentair kit that is easy to use but uses more reagent. Today I tested using that kit twice and both times got 90-95ppm. I tested with the TF-100 /Taylor kit and got 65-70ppm.. Not sure which to trust.

Maybe the Pentair reagent is old...I could try using the Taylor reagent using the Pentair tube and see what that says but for now I'm going with 70ppm since the yellow algae SLAM worked at approx. 40 ppm which was the 1 gallon of 11% CL I put in at 11PM.
 

Oly

Gold Supporter
Jun 28, 2017
1,676
Fresno, CA
Pull it out and have a look around inside. As you know you can clean the light fixture outside of the pool. The niche may have to be scrubbed a few times and exposed the the high FC pool water. This area is a common safe zone for algae and one possible source of reoccurring algae blooms.
 

mgtfp

Bronze Supporter
Mar 5, 2020
473
Melbourne, Australia
Are you sure that that's all algae, not pollen or other stuff flying into the pool? I'm a bit surprised that algae keeps growing at these FC levels.

In regards to the CYA test, I'd trust the Taylor test, I don't know the Pentair kit.

Best would be to do an Overnight Chlorine Loss Test to get a baseline.
 
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Macysumo

Silver Supporter
Jun 27, 2020
37
Pensacola Florida
I'm thinking the niche is indeed the issue. My current hypothesis why I can't rid it from my pool: "When it rains hard, there's hydrostatic pressure pushing on that niche and forcing algae spores into the main pool."

Cleaning the niche carefully today. We'll see if my guess is right. Rain is headed our way all weekend.
 

Macysumo

Silver Supporter
Jun 27, 2020
37
Pensacola Florida
Opened up the niche (with some effort, I'll explain later) and a huge cloud of brown "dust" came out. A run around the niche with a brush and another huge cloud of brown Crud flew out of there.
Let it settle for a while then vacuumed to waste what yellow algae and particles were on the bottom. Checked the Free Chlorine and it was at 29.5 ppm and CC 2 ppm, so at SLAM level but not mustard algae level.

Have to add some water and bring the FC back up to 30 then do the OCLT tonight... I suspect it won't pass given all the junk that may still be in the water but we'll see.

___________________

Question about the pool light. Let me know if I should post this elsewhere.... don't know if this is related to my yellow algae or if it's a bigger problem

When I went to unscrew the holding screw at the top of the pool light it wouldn't budge. I had to get a mask, get underwater and grab the screw head and twist it out. When I looked at it, it was degenerated, most of the threads were gone and it was in horrible shape. I had recently replaced the Pentair LED light assembly (I think no more than 3 months ago) as the bulb had failed and the old screw was also not in good shape so I replaced the screw with a stainless one from the local ACE hardware store. See the photo below.

I looked in the niche...there was a unconnected ground wire. The ground post was in the back but the ground wire had not been stripped or connected when originally installed in 2014. I'm not sure but since it's 12Volt and not 120Volt maybe it doesn't need a ground. Can anyone help here? Could this be germane to my algae problem? The "rust" from the metal loss as fuel for the algae??? Or, the "dust" it the niche was really rust from the metal? Seems wrong it was just rust in there.. too much material came out when I opened the niche.


IMG_3584.jpeg
 

Flying Tivo

Well-known member
Jan 24, 2017
1,895
Monterrey, NL, Mexico
The rust was probably due to low Ph when the pool guy was managing it with pucks which are acidic. Yes ground the light and put new SS screw. Make sure you still leave the niche open while in slam mode and brush regularly inside.
 
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Macysumo

Silver Supporter
Jun 27, 2020
37
Pensacola Florida
Rained really hard today. Had to pump to waste as pool was getting to the emergency overflow drains. Added another 32 oz of 11% Chlorine and got the pool back up to 41 ppm FC with 0 CC and TA 80. Mustard algae on the floor appears dead. Do I let it stand another 12 hours then vacuum to waste or do it now? It's not clear in SLAM to my reading when to vacuum the dead algae up?