White Water Mold

Jun 4, 2012
Pittsburgh, PA
First of all, if this has been discussed before, please point me to the appropriate thread.

This season, I've seen more cases of people having white water mold in their pools than any other year. Last season we had maybe two people reporting the problem. This season there have been over ten people.

So what is white water mold? Is it truly a mold? Or is it a "pink algae" type deal where it's just a misnomer?

Any ideas what's causing this for so many people this season? Is it environmental? River/Lake-based? Are people spreading it from pool to pool?

It's frustrating for me to see this same issue affecting so many people.

Also what's the best treatment method (in your experience) for something like this? Would the addition of borates do anything at all for this?


Mod Squad
TFP Expert
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In The Industry
Apr 1, 2007
Sebring, Florida
Adequate chlorine is ALWAYS the answer for things growing in a pool. I found some mold in my light niche a couple of years ago and mechanically removed it but it got there because my chlorine was inadequate.....I hadn't cleaned the niche in four years.

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
San Rafael, CA USA
We rarely see white water mold in properly chlorinated pools. White water mold is a fungus and has some similarities to yellow/mustard algae in that it prefers shady areas with poor circulation. It has similarities to biofilm in that once established it forms a protective coating that is difficult for chlorine to penetrate. The key, therefore, is to kill it before it gets a chance to take hold. The treatment for an existing outbreak is somewhat similar to that for yellow/mustard algae except that it doesn't take as high a chlorine level. Instead, one gets behind light niches, under removable ladders, puts in all poles, nets and other equipment into the pool, and shock the pool at normal shock levels (if you wanted to use yellow/mustard algae shock levels, you can, but it's not necessary). That along with physical removal is usually sufficient.

The use of 50 ppm Borates as a weak algicide will help to prevent it, but is unnecessary if you properly maintain the appropriate Free Chlorine (FC) relative to the Cyanuric Acid (CYA) level. So the borates should be seen as insurance, not really needed.

What were the current and historical FC and CYA levels in the pools that have this white water mold?
Jun 4, 2012
Pittsburgh, PA
I can't recall everyone, but typically, the chlorine level is nonexistent at the point where symptoms are presented. Stabilizer tends to run a little high as well. Neither of these are across the board, but, perfect storm I suppose. I'm just not sure why this season is so riddled with this problem when the "my pool won't hold chlorine" complaint is and has been a common thing.

When you say "one gets behind light niches" do you mean you should brush areas where light doesn't reach?


Active member
Jul 6, 2011
Chambana, Illinois
Before I converted my pool from Bacquacil to chlorine, I fought white water mold/pink slime for 4 years. I observed (at least in an anecdotal fashion) a relationship between my water temperature and white water mold blooms. My family and friends like to swim in very warm water (90-95 degrees). It seemed that every time I ran my heater to bring up the temperature from mid 80s to (occasionally) mid 90s, I would get a while water mold bloom within a day or two. [Obviously the fact that I was running the heater meant that we were getting ready host swimmers and thus our bioload went up along with the temperature--which certainly would contribute to any biological outbreak as H202 (hydrogen peroxide--Bacquacil Oxidizer) was being consumed at a higher rate anyway.]

rbarba, I see you are in Pittsburgh. I am in Central Illinois. Did you have as warm a spring (especially March) as we did? I opened my pool to heavy algae and a touch of papery water mold in the skimmer in mid April. I wouldn't be surprised if the warmer temperatures this year might be a contributing factor to the increase in outbreaks you observe.

The solution, of course, is to go through the shock process. I was meticulous with my opening shock process and was up and running in a week.

EDIT: It was a VERY warm spring: http://www.crh.noaa.gov/eax/?n=clm_spr_may2012
Jun 4, 2012
Pittsburgh, PA
Sorry for the delay here.

Yes, Matt. The temperature spiked to the 80 degree range in February. (Then it was way too cold in the beginning of June, but that's beside the point). I was thinking everyone's safety covers being on made incubators out of all the pools.

I was hearing something about the warm temperatures causing biofilm to develop, which facilitates the growth of the mold? I'm in the dark about the topic of biofilm so I can't really speak to the credibility of that.

My mistake. It was March, not February. From the 21st to the 23rd, average temps were high 70s to low 80s.