Mustard Algae?

bbasarich

Member
May 24, 2021
13
Edwardsville, IL
Pool Size
16600
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
I'm trying to determine if I have a mustard algae problem or something else. Last Friday I noticed about a 6-ft long section of brownish/green along the coped (45 degree) surface that meets the deep end of my pool. This side of the pool is mostly in the shade now from trees, etc. It easily brushed away and and I vacuumed to filter and then backwashed. The next day, in the same spot I noticed 1-foot strip the same color residue start to form. Here's a picture:

InkedIMG_0415_LI.jpg
It's a vinyl liner pool, and you have to really zoom in to see it ... look at the white "grout" lines and notice the discoloration. I looked around the rest of the pool and found a couple other similar areas that had the same discoloration. Here's another pic on the opposite side of the pool:
InkedIMG_0417_LI.jpg
You can see the discolored on the partial tiles along the seam.

Thinking it could be algae, I started a SLAM on Saturday. My tests (using TF-100 test kit) from Saturday morning were:

FC 5.0
CC 0.0
pH 7.7
TA 90
CYA 40

I added liquid chlorine to raise the FC level to 16 (after reading some more, I realized I should've lowered my pH first). I brushed and vacuumed to filter on Saturday and restested/added chlorine every 1 to 2 hours to keep up FC. I did an OCLT Sat night/Sun morning, but obviously messed up the Sat night test because I had 13.5 Sat night and 15.0 on Sat morning ... I blame drop counting fatigue on the Saturday night test.

On Sunday, I continued to test and keep FC up at 16, and brushed and vacuumed again. Performed the OCLT test, this time testing twice on Sunday night - 16 FC, and twice this morning - 15.5 FC and 0.0 CC. So I think I passed the chlorine loss test.

However, looking at the hot spot in my pool this morning, I can vaguely see the discoloration starting again.

Could this be mustard algae? With the little chlorine loss and no CCs, I'm at a loss. Starting this week, we've started to have a lot of leaves fall in the pool, so I'm constantly emptying skimmer baskets and skimming the pool. But if from the leaves, I wouldn't expect the discoloration to keep forming in the exact same spot.

Any advice?

Thanks in advance.
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2014
33,636
Texas, San Antonio/Marion, South-Central Area
Pool Size
17888
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-45 Plus
Really hard to tell what you have going on there. You did pass the OCLT, but that doesn't resolve Mustard Algae (MA) spores if there are some. So if you still have time before closing, you could increase to SLAM level, perform one more OCLT, and if you pass increase the FC to MA level (24) for 24 hrs only. If it is MA that should resolve it.

 

bbasarich

Member
May 24, 2021
13
Edwardsville, IL
Pool Size
16600
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Thanks Texas Splash. I didn't add anymore chlorine last night and did another OCLT and passed (11.5 FC to 11.0 FC in the morning). I did, however, find another spot with the residue near the other hot spot area. I raised my FC to 27 (the CYA test is so subjective, I may really be somewhere between 40 and 50), brushed the spots I found, and then threw all my pool cleaning equipment in the pool. I'll keep FC up at MA level until tomorrow morning and see what happens.

Thanks again!
 
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bbasarich

Member
May 24, 2021
13
Edwardsville, IL
Pool Size
16600
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Just wanted to follow up. Raising to MA SLAM level for 24 hours seems to cleared up the issue - 2 days without any growth in the hot spot and water it clear. I'll continue to monitor and let FC drift down to normal levels.

Thanks again Texas Splash! I'm a first time pool owner - first season - and just needed the extra nudge to treat as Mustard Algae.
 
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Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2014
33,636
Texas, San Antonio/Marion, South-Central Area
Pool Size
17888
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-45 Plus
full
 

TxPoolGrl

Member
Jul 1, 2021
18
Texas
Pool Size
24000
Surface
Plaster
Chlorine
Liquid Chlorine
Just wanted to follow up. Raising to MA SLAM level for 24 hours seems to cleared up the issue - 2 days without any growth in the hot spot and water it clear. I'll continue to monitor and let FC drift down to normal levels.

Thanks again Texas Splash! I'm a first time pool owner - first season - and just needed the extra nudge to treat as Mustard Algae.
What is ma slam level, I have the same brown green powder in spots of my pool, I’ll brush and they go away and next day back all where the side meets the bottom and some on the floor
 

bbasarich

Member
May 24, 2021
13
Edwardsville, IL
Pool Size
16600
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
MA for Mustard Algae SLAM level. After a normal SLAM, I had to elevate my free chlorine to even higher level for 24 hours to resolve the mustard algae problem. For my CYA level 40, I had to raise FC to 24 (I actually raised to 27 since my CYA is more like 45).

See the post here Chlorine/CYA Chart for mustard algae SLAM levels.