Mustard Algae?

[jparr]

I have recently begun maintaining my pool after repeat lackluster performances by our pool guy. There was black algae everywhere that I have scrubbed with a stainless steel brush, pretty much eliminating it. Every now and they it will start to grow in some of the pitted grout around the tiles, but this is easy to kill with the brush and some bleach in a spray bottle. The yellow/mustard algae has been a lot more problematic though. When first taking over the pool, I shocked it at 40+ ppm chlorine for a week, scrubbing everyday and it appeared that the algae was gone. There were still some yellow areas, but I could not tell if it was staining or algae. In some places our plaster is very rough, and the scrub brush doesn't get in to the little nooks and crannies. After shocking and scrubbing, I backwashed the DE filter (actually completely disassembled it and thoroughly cleaned it) My CYA has been as high as 100, but I am slowly lowering it, draining about 10% of the pool every weekend and refilling.

FC: 9-15 (one 128oz bottle of 5% every night)
CC: 0 (with an occasional jump to .5 if the FC drops to the low end after excessive rain or hot sunny days)
PH: 7.4
TA: 120
CYA: 80
CH: 460

http://www.flickr.com/photos/jparr/sets ... 433681083/

The pics show both the north and south sides of the deep end. The south side is shaded most of the day, and home to most of the algae, while the north side gets direct sun and has very little algae.

 

[frustratedpoolmom]

Sure looks and sounds like MA.

See this chart:
http://www.troublefreepool.com/chlorine-cya-chart-t2346.html

It gives your "min" for mustard algae and also your shock level.

I'd recommend taking it up to your shock level, brushing the heck out of the problem areas. Then for 24 hours take it up to the MA shock level on the chart. Be sure to treat floats, toys etc. and wash suits and towels in hot soapy water. Check light niches and ladders etc.

Then run with the higher "min" level for a few weeks - see if that can erradicate it.

 

[jparr]

Would increasing the water movement in this area help at all? The drain is currently clogged, but I plan to attempt opening it up soon.

 

[frustratedpoolmom]

Yes, improving circulation always helps, as does increasing overall run time along with the FC level. But if this is true MA it's resistant to "normal" chlorine levels.

 

[jparr]

Just threw in 13 gallons of 5-6% (the quality varies) of beach and a pound of trichlor shock, which should push my FC up to 45ish. Poolcalculator says mustard algae shock level is 42 based on my CYA. I'll scrub for the rest of the weekend and see how it turns out.

BTW, as I was throwing away the bleach bottles, my neighbor ran up behind me and cannonballed in to the pool. I hosed him off and he looks ok, so apparently 42ppm FC isn't fatal.

 

[chem geek]

BTW, as I was throwing away the bleach bottles, my neighbor ran up behind me and cannonballed in to the pool. I hosed him off and he looks ok, so apparently 42ppm FC isn't fatal.

The pool was probably equivalent in active chlorine level to a pool with less than 1 ppm FC and no CYA so not much different than many indoor pools.

 

[jparr]

I've taken a second attempt at killing this mustard algae. My CYA level drifted down to 40, so since I had to add some CYA anyway, I decided to use up some of the granulated trichlor I have. On Thursday night I brought the FC up to 35 with trichlor/bleach, and the SWG on superchlorinate. The pump and the swcg have been running 24/7 at 100% since then, and the FC levels have been kept between 35 and 45. Tonight I will shut off the pump and swcg and test my overnight loss. After vacuuming 24 hours after maintaining shock levels I saw my filter pressure jump by 5 PSI, this is rare, so I assume this is dead algae.

 

[chem geek]

After vacuuming 24 hours after maintaining shock levels I saw my filter pressure jump by 5 PSI, this is rare, so I assume this is dead algae.

I hope you are right and am keeping my fingers crossed. Don't forget to expose areas that normally don't get much chlorine (if possible) since yellow/mustard algae likes shade and will come back if it survives behind light niches, under removable ladders, or on poles and other items that get reintroduced into the pool. Even if it survives somewhere, you can keep it away by maintaining a higher FC level that is around 15% of the CYA level, but that's inconvenient and also more expensive due to greater chlorine loss (mostly from sunlight) and therefore usage. So killing off this algae completely is the best way to deal with it, but can be a challenge.

 

[jparr]

UPDATE: Re: Mustard Algae?

It has been about a month since the shocking, and the mustard algae has stayed gone. The water temps have also dropped by almost 10*F, so that certainly doesn't hurt. I have been keeping the FC levels between 8 and 10, with a CYA of 60. The chlorine demand has dropped considerably, not sure if this is due to the lack of algae, or the temperature drop. My CircuPool RJ45 used to run for 9 hours a day at 60% to keep up, and it is now at 20% for 7 hours a day. My CYA was also increased by about 10PPM while shocking, so this may contribute to the lessened chlorine demand.