Another Algae Question....

[mpacheco72]

So I passed the OCLT night before last, but I still see algae on the floor of my pool. It won't scrub off with a nylon brush. Last night I got into the pool and with a butter knife scraped at some of the spots on the floor. They look black but when you get it to start coming up on the knife they are a very dark green that when smeared is a green slimy substance. So I've been told that I can't have black algae because I have a vinyl pool liner, but I can't figure out what else this may be. I've scrubbed and scrubbed for two weeks and although it's made some difference (and keeping the pool up above shock level) there are still some spots left. What are your suggestions?

FC=17.5
CC=0
PH-7.4
TA=170
CH=390
CYA=40

 

[duraleigh]

So I've been told that I can't have black algae because I have a vinyl pool liner

"Can't" is probably not correct but "very unlikely" is.

Black algae seems to show up on pools that have been badly neglected for a long period of time. and almost always on plaster pools.

That said, I agree it sounds like black algae so what I would do is simply more of what you have been doing. You must mechanically expose the insides of the black algae by brushing them or scraping them off as you have done. Secondly, since the waterborne algae is cleared up, I would run the FC at about twice the normal level......if your CYA is 50 than normal would be around 4-6ppm, I would run it 10-12ppm. You must do this continuously until the there is no sign whatsoever of the algae.

Importantly, continue the mechanical removal of the spots. It is forming a tough biofilm on it's outer surface that protects it from the chlorine so you must remove that biofilm to kill the algae continuing to grow underneath.

It may take a pretty good while (weeks) to get this done but I think it's the only way to be successful.

 

[mpacheco72]

Thank you, Dave. I was beginning to go crazy thinking it looks like black algae it acts like black algae but it can't be. I can tell you that I was able to remove about 50% of it last night. So it looks like I'll be jumping back in tonight with the butter knife. And yes, the pool was neglected most of last summer and horribly over the winter. I've learned a hard lesson.