thought I had killed the mustard, but no.....

[rhythm]

Well, I thought I had done things right last time when I attempted to get rid of the mustard, but evidently I didn't. I'm pretty darn sure the stuff is mustard, as it started in the mouth of the skimmer, and then appeared in pool/spa light areas and on the sides of the pool where it's shady.

When trying to get rid it a few months ago, these were the numbers:

pH: brought it down to 7.2 before shocking with liquid chlorine (normally 7.4 - 7.8)
TA: 70
CH: 350-375
CC: 0
CYA: < 30 (30 is the top mark on my test, and I could still see the black dot)

I brought the FC up to 30 ppm to begin with, and kept it between 25-30 ppm for about 4 days. I brushed a LOT during this time as well. After that I let it drop to around 20 ppm for another day or two. Then I verified that it was holding overnight so I stopped adding chlorine (it may have been holding overnight earlier, but I hadn't checked yet). I tried to make sure that I kept the FC at least 4 ppm for the next several weeks.

Things looked GREAT. For a couple of months I didn't see a hint of the stuff anywhere. I was HAPPY! But then I started noticing it in the skimmer again, and I knew it was back. There may have been a day here and there that the FC dropped to 2 ppm or so, but for the most part I've kept it higher. I get the feeling that I didn't get a new infestation, but that I didn't really get rid of it all the last time I tried. But of course I could be wrong.

I'm wondering if I've overlooked some things in getting rid of the algae. How often should I be backwashing my DE filter when doing this? Could I be re-introducing it with things like the hose, brush, pole, net, or vacuum head? This time around I may also remove the main pool light, as I may not have been able to brush some algae off from under the metal ring. Anything else? Should I do the same thing but for a longer period of time? I'm due for a complete DE filter cleaning (I like to take it apart and clean the grids each 6 months). Should I do that before starting the next attempt, or should I shock and brush for a while, then completely take apart the filter and clean it?

My numbers are still the same for TA, CYA, and CH. I wasn't going to bring the CYA up for the Summer until I had finished attacking the mustard again. My pH varies between 7.4 and 7.8 (it's always wanting to rise and I bring it down a couple times a week). I'll bring it down closer to 7.2 before shocking. Currently my FC is 4-5 ppm. That level is keeping the mustard from getting much worse before I attack it again.

Any suggestions would be greatly appreciated.

Thanks,
Greg

 

[tagprod]

If things looked great for a couple of months, I'd bet you killed it the first time and you have a new infestation. Not sure about reintroducing it with the pool brush or other things. I wouldn't think it would live very long outside of water, but that's just a feeling.

 

[rhythm]

Thanks for the reply Brian. Perhaps I did get a new dose of it. I thought that keeping around 4 ppm of FC with the CYA under 30 would have kept a new infestation away, but perhaps not. I was thinking that perhaps I just didn't get every last little bit of it killed, especially if there's some hanging out behind my pool light ring (I'm going to remove it this time to be sure). I didn't do much backwashing of my DE filter, so I'm wondering if someone can advise me on that...whether or not it's crucial. Anyway, I'll be starting a new attack on it this weekend.....I really hope I get rid of it and keep it away for good this time!

Thanks,
Greg

 

[duraleigh]

Briefly, mustard algae requires more chlorination than normal to keep it from returning...regardless of the source.

With a CYA below 30, I suspect your FC level has dropped too low from time to time and allowed the algae to regain a foot hold.

If you'll bring your CYA up to around 40ppm or so, your FC level probably wont yo-yo as much and it will be easier to maintain it at a maintenance level of around 5-8ppm which most likely will keep it at bay.

 

[rhythm]

Dave, I agree....I'm going to bring my CYA level up this weekend. For a couple of months after hitting the mustard last time we were in a part of the year where the FC was pretty undisturbed by the sunlight and the FC level was holding pretty well day to day. But I got too comfortable (lazy) and when the weather warmed up a bit and the sun got higher overhead the FC must have dropped long enough for the yellow to return.

We're just starting our second season with the pool, and I'm finally starting to "get it", in that I need to keep a higher level of FC in the pool than I originally thought that I needed to, and that even a one day drop below the proper level can have consequences!

Thanks again,
Greg