High CYA, Mustard algae, drought

balagon · May 18, 2009

Not a happy situation here. My pool has had a mustard algae attack. The usual TFP prescription is to measure FC and CYA, and then use the pool calculator to figure out how much chlorine to add to get the FC level up to mustard algae shock levels. FC is at 6.5, and CYA is at 80. As the Pool School course in battling algae says, " If your CYA level is too high, you will need huge amounts of chlorine, which rapidly becomes impractical". Well, the pool is at that point--target mustard algae shock level for the pool is 44 :shock:

and I'd need to put in 10.5 lbs of 73% cal-hypo or 15 gallons of bleach. :shock:

I know, mea culpa, mea culpa, my fault the pool got to this point. Forgive me, forum, for I have sinned.

Alternatively, the pool calculator tells me that I should drain half the pool and then refill with fresh water. In any other year, that's what I'd do. Except that this year, California is having a serious drought. Come June 1, we'll be subject to water use restrictions, including a ban on filling pools. Technically, I could still get the pool partly drained and then refilled, but the thought of doing that right now just feels wrong. I really don't want to waste that water, especially as lawns are going brown. Especially as the pool is due for a replaster job, which we are hoping to do in the coming year, which would mean that we'll be draining and refilling the pool at that point.

I'm curious to know what people recommend that I do. Is it worth it to put in that huge amount of chlorine and get the pool up to that high shock level for three days? If I do that, and then put in the requisite chlorine religiously, will that truly keep the mustard at bay for the season? Or, should I just limp along with weekly brushing (I know my habits, there's no way I'm going to be able to do daily battle with it) for the rest of the season? What words of wisdom do the forumites have for me?

JasonLion · May 18, 2009

The very first thing to do is to be sure you really have mustard algae. Probably 2/3rds of the people who think they have mustard algae actually just have pollen that happens to look like mustard algae.

If you really do have mustard algae, you have a problem. Mustard algae is known for coming back. One trip to high shock level isn't always enough. But lets put that off till you are sure you really do have mustard algae.

balagon · May 18, 2009

I really do have mustard algae. Too dark to go out and take a picture now, but I've done battle with the foul beast before. It's primarily on the walls, not floating free...I'm raising my right hand and swearing that yes, it's MA. :-D

JasonLion · May 18, 2009

To reliably kill mustard algae, you need to use high shock level, and brush absolutely everywhere more than once, and soak all pool tools and toys in the pool while it is at high shock level or wipe them down with a dilute bleach solution, and wash all swim suits. And every once in a while you still miss something and it comes back anyway. The process is more reliable if you have borates in the pool, but even that is no guarantee.

reebok · May 19, 2009

I would imagine LA has plenty of pool stores and liquid chlorine, which may be easier than bleach (would require less anyway). I have had mustard algae many times ("where is this yellow dirt on the bottom of the pool coming from?") among other problems. it was before I knew about this site, and I used stop yellow from the pool store. it seemed to work ok and if you want to use lower levels of chlorine, that may help. but the others here may tell you why that's a bad idea.

balagon · May 19, 2009

Jason, is it worth it to try adding borates at this point, in order to drive down the amount of chlorine I'll need to add? Or is it not useful unless/until the pool is clear of algae?

JasonLion · May 19, 2009

You could go ahead and add borates. They will help, though as I said they don't guarantee sucess.