Yellow algae I assume


Well-known member
Jul 23, 2014
East Texas
I need the Winston Wolf of pool water here. I've been fighting yellow algae for weeks, or at least I'm assuming that's what it is, it's a yellow/brownish substance that looks like dirt. I've tried everything to get rid of it and I can knock it back for a while but it comes back within a day. I've tried every kind of Yellow out, yellow whatever and none of those specialized chemicals seem to work to completely get rid of it. I brush the pool at least 3 times a day, pump running 24x7, backwash once a day (it's a DE filter) even vacuuming up the bottom directly to waste. Nothing completely gets rid of it, I've also tried SLAMing it multiple times (20 ppm) but it always comes back. A picture is attached, it likes to form around some of the rough plaster patch edges on the bottom of the pool. My ph is around 7.0/7.2, it tends to be lower because of all the chlorine I add, I mostly use the liquid stuff to SLAM it. Alkalinity is around 80, cya around 50, FC around 3ppm unless I'm adding more as required by some of the yellow out chemicals. Is there anything else I can do? Is draining the only option and then I don't know if even that will work.



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Gold Supporter
Bronze Supporter
Jun 11, 2018
Verona, MO
With CYA of 50, your target is 6-8 ppm. Absolute minimum, which you don't want to be at very often is 4ppm. So if you run your normal FC at 3, you are leaving yourself open to algae.

Chlorine shouldn't affect your PH much, if at all. Are you using pucks or something to add acid?

Not sure what yellow out is, but if you follow TFP slamming and maintaining, you shouldn't need it.

What test kit are you using? Add that to your signature too please.

Good Luck!


Bronze Supporter
You need to do a mustard algae SLAM Process. Do the typical SLAM until you pass Overnight Chlorine Loss Test, then increase your FC to the appropriate level for mustard algae for your CYA and keep it there for 24 hours. You can find that level in the chart in this post. I had an outbreak of mustard algae earlier this year, and that cleared it right up. Be sure to put all your equipment and toys in the superchlorinated water for 24 hours as well, and wash the swim apparel.
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Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
Laughlin, NV
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
What Yellow Out products have you used? Some are sodium bromide. Which turn your pool in to a Bromine pool.


Gold Supporter
Bronze Supporter
Jun 29, 2016
Tampa, FL
Pool Size
Salt Water Generator
SWG Type
Intex Krystal Clear
Do you have your own test kit? If not, you need one, like the one in my signature. You can’t really proceed unless you know your numbers, and pool store tests are not reliable.

When you say you’ve SLAMmed multiple times at 20ppm, what do you mean? To SLAM is to test every few hours for more than a day, raising FC to SLAM level each time. When you SLAM successfully, your water is crystal clear with no visible algae, you have CC of 0.5 or less, and you pass the Overnight Chlorine Loss Test (OCLT). Then you let your FC drift back down to target, which is at least 6-8 if your CYA really is 50. Letting it go lower is asking for a repeat algae bloom.

I feel like a lot of what people assume is mustard algae is really just regular algae that wasn’t completely eradicated due to ending SLAM prematurely, or a repeat bloom because they stopped maintaining proper FC levels. Nothing wrong with following mustard algae protocol at the end of SLAM, if you aren’t sure.
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