Mustard Algae questions

stevenfex

Active member
May 1, 2021
36
orange county, ca
Pool Size
17000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool Edge-40
I just purchased enough chlorine to complete the mustard algae slam procedure, but I have some questions before I do it.

I slammed about 6 weeks ago after the pump died and algae bloomed for several days, but I did not do the mustard procedure which I am now 100% sure I have (mustard yellow streaks spread on walls and shady areas of pool, zero effort to brush away, robot picks up gray soot which I assume is dead algae). It 'feels' like it's relatively held in check due to the FC in the water but obviously I want to fully eliminate it. Tt takes a few days without brushing for it to become fairly noticeable in the same shady areas of the deep end.

Numbers as of yesterday:
FC - 7
CC - 0
CYA - 50 (getting more to raise to 70-80 after slam. little flooding mishap dropped this from 80 to 50)
CH - 350
TA - 140 (I think my fill water is high because this was 120 before the flooding - I plan to do the low pH and bubble procedure soon)
pH - 7.8 but quickly creeps up due to algae.
Salt - 3600

1. Is it sufficient to just backwash my DE filter after I complete the MA slam?
2. Is any introduction of mustard algae in the future going to mean I have to do this again? I hope not, but I plan on disinfecting everything, laundering swimsuits, etc. to at least limit the chance.
3. Once complete and I get my CYA back up to 70, should I hold a higher FC level of 6-7 vs. the typical 5 recommendation?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
43,992
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
You must complete the normal SLAM Process first. Please read Mustard Algae - Trouble Free Pool

1. Yes
2. Possibly. MA can be persistent. Following the procedure linked above is the best way to manage that.
3. Read the linked MA process. Chlorine/CYA Chart Note the Yel/Must FC Min column. That should be your minimum FC for several weeks after your 24 hour MA shock.
 

stevenfex

Active member
May 1, 2021
36
orange county, ca
Pool Size
17000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool Edge-40
Yup, normal slam first. I'll raise to 20 FC first, pass SLAM, then 30 for 24hr to shock the mustardo. I'll follow that minimum mustard level as well. I was just looking in the main FC/CYA chart so never noticed that.

Any reason to hold off adding CYA for a month or so to keep my FC requirement lower or would it likely end up around breakeven w/ the higher CYA level better maintaining the higher FC?

I will check my fill water TA to be sure it's high, as well.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
43,992
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
I would not raise the CYA until you complete the SLAM process. And even then, at this time of year, the CYA level of 50 is likely fine as the UV impact on the water is starting to decrease. My FC use each day is slowly decreasing.
 

cmwerner

Member
Jun 7, 2020
10
San Jose, CA
Pool Size
18000
Surface
Plaster
Chlorine
Liquid Chlorine
Curious on the discussion of CYA upwards of 80. My understanding was that you don’t really want CYA getting much over 50-60 at the high end. What would be the reason to bring it all the way up toward 80?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
43,992
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
What would be the reason to bring it all the way up toward 80?
SWCG use in areas like Florida, Texas, Arizona can benefit from higher CYA.
 

stevenfex

Active member
May 1, 2021
36
orange county, ca
Pool Size
17000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool Edge-40
Re: 70-80 CYA, I'm just going by what the Pool School article says for recommended levels with a SWG.

I believe I also read a thread somewhere here where someone tests a lower and higher CYA and found that their SWG could be run slightly lower at the higher CYA level, even though the overall FC target was higher.

I do wonder if it's worth it though if you account for having to SLAM the pool even once a year or something, especially in a bigger pool. Even at 50 CYA it still took a bunch of liquid chlorine and a good amount of MA to drop the pH before the slam.
 

stevenfex

Active member
May 1, 2021
36
orange county, ca
Pool Size
17000
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
CircuPool Edge-40
Just to update, mustard algae has not returned. Fingers crossed.

I was getting a low salt level on 8/25. I backwashed the filter and been OK since then. I'm not sure if it's common but it seems like while I had the algae my SWG was going haywire with either low salt or low flow readings, and I wonder if it had to do with the filter getting clogged really quickly w/ dying algae. I'm sure higher TA wasn't helping either.

8/26 passed OCLT, bumped FC to mustard slam level 30
8/26 at7pm FC was 24, bumped back up to 30 and cranked SWG
8/27 did not test but added another 1/2 gal chlorine that morning
8/28 at 11pm, FC was 26. Fairly confident I had 24hr of >30 FC, so mustard slam complete
8/29 FC 21 (SWG at 4)
8/30 FC 16 (bump SWG to 6)
8/31 FC 18
9/1 no test
9/2 FC 22 (SWG at 6 was adding +2 FC daily. Dropped to 3)
9/3 just now FC 16, super intense sun. Bumped SWG to 4 will check again tonight.
 

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