Beginner who inherited mustard algae! Story/HELP!?


New member
Jun 4, 2020
Columbus, OH
New pool owner looking for help/advice with the mustard algae:

Bought a house with a pool in Sept 2019 with no experience
Inherited a mustard algae problem
Found TFP after spending hundreds of bucks at the pool store
Couldn't dump enough chlorine in to get to an OCLP < 2ppm over 12 days.
Couldn't even prevent it with a massive dose of Polyquat 60 before it started.
The only thing that seems to have worked is starving it of Phosphates (Dammit!!)

Bought our house in Sept 2019 and had no idea what to do with the pool, but the water was crystal clear when i took it over.
Here's my story so far:

1: Immediately got on r/pools to try and figure everything out
2: Found TFP and decided that I have a TON of research to do that can't be done in the 4-6 weeks before I have to close this thing.
3. Drove to the big-name pool store that was close to my house and bought $300 worth of trichlor/dichlor :)
4. Cranked the heat to 89, put a couple pucks in a floater, swam around, and thought I was good.
5. At this time CYA was 40, FC was ~4-5 (from my pool store test results)
5. All of a sudden I got mustard algae.
6. The internets said I most likely didn't have mustard algae, and I'm new at this, so I thought I must be crazy.
7. Mustard algae went away once the water got below 65 or so.
8. Closed the pool in November with a waterproof/tarp winter cover.

9. Did a bunch of research over the winter about pool chemistry (TFP included)......
10. Did a bunch of research on mustard algae
11. Convinced myself that I can get away with trichlor pucks / dichlor shock because I have a short swim season in Ohio, I have a sand filter that I can backwash, and my pool is only 14k gallons.

12. Opened the pool myself right around Memorial day to a CRYSTAL CLEAR POOL, everything was in check except TA and TH, they were low.
13. Took a sample to the pool store and they measured { CYA: 24, FC: 2.45, TC: 2.62, pH: 7.4, TA: 57, TH: 120 }
14. The only thing I did right away was dump a half-bottle of Polyquat 60 in as a preventative measure (didn't want even a hint of what I presumed to be mustard algae from last year)
15. LOST money by trying to SAVE money by calling off work to run-around the city to try and find enough baking soda to make a dent in my TA.
16. Concluded I lost many hundreds of dollars via opportunity cost by running around aimlessly in search of cheap chemicals :)
17. Decided you're all a bunch of quacks :) JK, love this place.
18. Floated 2 pucks and kept 5ppm FC for a couple weeks and thought I was gold!
19. Bragged about how easy it was to a bunch of people
20. Had a few friends over to swim...
21. It was right around here that the sun finally came out in full force and PUT ME IN MY PLACE.
22. A few days after the guests were over (full UV over these days), my water was looking ever so *slightly* cloudy so I decided to check it.
23. Measured 0ppm FC with my Taylor 2005 kit the previous owner left me, (hindsight: it had probably been @ 0 for a good couple days).
24. Tossed 2lbs of dichlor in that night. (Brought me > 5ppm.)
25. Woke up with crystal clear water, but also the beginnings of the same mustard algae I recognized from 2019.
26. Tossed another 1lb dichlor in and added a puck to the floater (for total of 3 pucks). (back up to > 5ppm)
27. Next morning was back down to @ 0ppm, so added another 1lb dichlor. (And back to > 5ppm)
28. Next morning back to 0ppm

.... Uh oh. Back to TFP boards, what do I do?....

29. Ordered a 2006 kit so I can measure FC more accurately, 1-day delivery on Amazon
30. Drove to find and bought 24 gals 10% bleach
31. Bought a bunch of cal-hypo shock
32. Brought the pool up to 18ppm FC with combo of bleach and cal-hypo.
33. About 6 hrs later was down to 12ppm.
34. Started measuring FC/CC every 6 hours...

35. Started and continued to SLAM
36. 7 days straight of 1ppm/hr FC loss during the day with ~35-40 CYA (personal Taylor test AND pool store confirmed)
37. Only once did it dip down to around 5.5ppm because I had to leave town, and it was only that low for less than a couple hours.
I would shock to about 18 and let it fall to 12-13ppm on average. Checking it 3 times/day. I had to order the 16oz bottle of R-0871 to keep up.
Still, 1ppm/hour loss during the day, which slowed to 2ppm loss OCLT (12am - 6am), EVERY night.

.... (Vacuum to waste, rinse, brush, chlorinate, let settle, vacuum to waste, BACKWASH, rinse, repeat)....

38. Started feeling defeated
39. Found a bottle of "Thio-Trine" that the previous owner left behind so I put my tin-foil hat on.
40. I thought maybe he was battling this yellow devil right before he sold me the house, dumped a bottle of "YELLOW-Trine" in to clear it up for the open house, and now I have a BROMINE pool.
41. Slyly asked the previous owner if that could possibly be the case, but he put that conspiracy theory to rest.

42. Gave in and bought a big bottle of Phosfree to try and starve it out.
43. Grrrr... I didn't want it to work, but like 1 day later it seems it did, and now I'm only losing 2ppm/DAY. (From 1ppm/HOUR)

So... I dunno... It was around 12 days of adding chlorine 3x/day to keep it around 15 ppm and I never got to a point where my OCLT was < 1ppm loss.
The yellow algae was still growing in the deep end the whole time.
Now, I didn't go to the very bottom to collect the sample, BUT I did go nuts and took 1ft measurements all around my pool so that I could 3D model it to find the exact volume in Autodesk Inventor in case my dosage calculations were off, and I was fighting a current with my measuring tape all the way to the bottom.
So I don't think it's a circulation issue.
And my single-speed pump was running 24/365 the whole time.

The yellow algae is no longer growing, my CC is consistently 0 or at least < 0.5, and my OCLT is now < 1ppm so I believe I can now FINALLY start my yellow-algae level shock @ 24ppm (rounding CYA up to 40) for 24hrs, put everything in the shallow end for disinfection, and hope that I never have to deal with this monster ever again!

Inground 14x28 poured concrete
Installed in 1957 by the original owner (he was a mason by profession)
Hayward 1HP pump
Pentair 400k BTU heater

My background:
I have just enough chemistry knowledge to get myself into trouble...
BS in Electrical Engineering (Had to take a few somewhat-difficult chemistry courses that I can barely remember. At the very least, all of my titrations were spot on, so you can at least trust my Taylor 2006 numbers )


New member
Jun 4, 2020
Columbus, OH
Curious if I'm doing anything wrong...? Kinda glad I had to deal with this so soon because I've learned a LOT! Just wish I could've killed it with chlorine alone. Or maybe it was just a coincidence. The thing that throws me is that it was still growing @ > 10ppm FC. Much higher than the Yellow Mustard min for my CYA level.
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