Mustard algae experience

[jhm]

After reading through the "Yellow/Brown dusty deposits that reappear repeatedly" sticky, I thought I'd discuss my experience and see if I still have a problem.

Over the last 3-4 years I've battled this algae. I always blamed it on myself (and rightfully so), because I let the FC get too low in warm weather. I would then get an outbreak, have to clean it up and be more religious in my maintenance.

The thing is once a spot in the pool has had an outbreak, that spot seems more and more susceptible to another outbreak. In fact, if the FC even gets low in warm weather, I know just where to look to see if anything is brewing. This has lead me to wonder whether I've really killed it before, and if it somehow still has hooks into those locations in the plaster.

With routine testing and adjustments, the water looks and feels great. But it is always in the back of my mind. Any thoughts by those who spent so much time thinking about and battling this nasty stuff?

Thanks!

[chem geek]

Yellow/mustard algae is more resistant to chlorine so needs higher shock levels to completely kill it off (roughly an FC that is 60% of the CYA level instead of the more usual 40% of the CYA level, but this is unconventional advice on this forum). It also likes shade so will hang out in light niches, under removable ladders, etc. which all need to be checked. Also, one must put in all equipment used to clean the pool (i.e. poles, nets, etc.) into the pool while shocking and should wash swimsuits in soapy water to prevent re-introduction.

[AnnaK]

Since you're able to identify specific spots where this algae tends to recur I wonder if you could try treating it with straight bleach? You could put some into a squeeze bottle (an empty mustard bottle, for instance) and squirt it directly on the spot. You could perhaps brush the area while you're treating it with the bleach.

This would be in addition to disinfecting the water and all equipment, of course. I'm just thinking that spot treatment, if possible, might be effective.

[PoolDoc]

From my experience with mustard algae, I think you'd be better to go with Chem Geek's advice. Spot treating certainly won't hurt, but having Scuba dived in pools with mustard algae, I can assure you that it's not only in places you see, but also in lots of others you don't see, including small cracks and crannies.

If you do hold the chlorine high for a while, be sure to brush thoroughly and then keep the chlorine high for at least a couple of days AFTER all trace of the algae is gone.

BTW, the Yellow Out (ammonium chloride) family of products do work . . . but at a price. You'll have a HUGE chloramine mess to clean up afterwards.

But, the Yellow Treat (sodium bromide) family probably don't work any better than simply raising your chlorine, and they will leave you with an unstabilized bromine pool after.

So, I'd suggest avoiding those -- no matter how miraculous the pool store makes them sound!

[jhm]

It also likes shade so will hang out in light niches, under removable ladders, etc. which all need to be checked.
Nail on the head there, those are the spots I'm talking about. So, maybe even though it is totally in check while keeping my water at good levels, I need to shock the heck out of it for a while to kill it off completely. Ben is probably right too, it's still living in places that I don't expect it, and will expose itself if I slip up.

Thanks!

[jhm]

One other thought, after a thorough shocking should I replace my cartridges, or can I get away with cleaning them? It ain't cheap to replace them. :)

[chem geek]

If you've got fairly even flow through your cartridges, the high shock level should be sufficient for killing algae in them. You could always clean the cartridges rather than replacing them. Algae won't like detergent, but it's really the chlorine that kills them.

[CarlD]

Yellow/mustard algae is more resistant to chlorine so needs higher shock levels to completely kill it off (roughly an FC that is 60% of the CYA level instead of the more usual 40% of the CYA level, but this is unconventional advice on this forum).

Richard,

What does this mean?
If CYA is 100ppm, recommended shock level is 25ppm--that's not 40%, that's 25%.
If CYA is 60-90ppm, shocking should happen at 20ppm--that's 33% of 60ppm and 22.2% of 90ppm.

The only place on the "Best Guess" table where I see 40% is when CYA is 30ppm and the recommended shock level is 12ppm--but the range for an FC of 12ppm is 30-50ppm of CYA. I don't see where JHM says the CYA is 30ppm.

So...what does raising from 40% to 60% of CYA mean? Does it mean increase the recommended shock level by 50% (12ppm becomes 18ppm, 20ppm becomes 30ppm)?

Carl

[chem geek]

You should move my post (or the part talking about FC % of CYA), yours and this one to The China Shop.

Ben and I disagree about shock levels so if you are using the Best Guess CYA chart the yellow/mustard shock level would be 50% higher as you describe. However, in terms of the amount of active chlorine (hypochlorous acid) in the water, the FC as a % of CYA tracks that better than the Best Guess CYA chart and in theory would provide the same rate of algae kill for shocking. Obviously, this becomes unwieldly at high CYA levels and in practice lower FC levels will still kill algae faster than it can grow though it will probably take longer to clear the pool.

The min. FC level for inhibiting yellow/mustard algae seems to be about double that of green algae, however, so I don't think the 25 ppm at 200 ppm is going to be sufficient to kill the algae. On the other hand, if your CYA is that high, the proper prescription is to to a partial drain/refill to lower it significantly. At shock levels, increasing the FC by 50% in the chart results in roughly doubling the active chlorine concentration so your "use 50% higher shock levels" would be reasonable.

Richard