Purple Rain

I have a question about, you guess it purple algae. To begin with I uncovered my pool and there was a lot of debris and green algae from our weird winter in Virginia. I have a mesh loop-loc cover on the pool.
My initial pool chemistry readings were FC 1, CC 1.5, PH 7.2, TA 70, CH 90, CYA 100+. I had all intentions to begin working on the pool and then the rains came, and it rained, and it rained and it rained. Since my CYA was way over the limit, I knew the only option was to drain off half the water. After I had already dumped 2 gallons of 8.25 % chlorine in, to begin slamming I did this over this past weekend, while battling more rain.. The water came this past Monday, while it was raining, again. On Tuesday I noticed a darker color of what I though was algae, I didn't get back to the pool until yesterday Wednesday. Here are my numbers. FC. 5, CC 0, PH 7.4, TA 50, CH 60, and CYA between 60 and 70. And now I have what I believe is purple algae. I can only assume the water delivery brought this in, the water came from the local fire department which is on public water. I had read that manganese could be the culprit, never had the problem before this! But before I go crazy buying chemicals I thought I would ask for advice here, it would be most appreciated.


Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Hello and welcome to TFP! :wave: Based on your last set of test results which were rather normal, I also suspect you have manganese in the water. You'll probably want to use a sequestrant like "Metal Out". You might like to read these threads if you haven't already:
Purple water??
Violet/purple Stains-entire pool surface

The last link has some recommendations from "SwampWoman" who is one of our foremost experts on metals treatment. I would also note however that your Frog System, if still active and being used, could be adding to the problem. I'll let some metals experts reply to that as well. Good luck to you!


TFP Expert
Mar 2, 2011
The copper from the frog and the high cyanuric acid point to copper cyanurate. What is your ph? Have you added ph increaser?


TFP Expert
LifeTime Supporter
In The Industry
May 20, 2007
SWSuburban Chicago, IL
maganese issues wouldn't show up like that that fast - I've never heard of a "purple algae". I recall once seeing some pinkish/purple looking stuff in my pool (years ago, before TFP ) but shocking/proper chemistry took care of it. Is the water purple? Or your seeing stuff on the bottom or what?

So to use the word algae - algae grows - if you are seeing dusty patches of stuff along the bottom of your pool (like all over) thats not algae... algae will grow along seams, in corners, on slopes or walls, etc when there is not enough FC from poor circulation, etc or not enough FC in general. And its usually green, or greenish yellow or greenish black. Now metals and metal staining behave much differently...