Trying to determine what type of stain/algae this may be

[douglasrlee]

Hi all! First post here.

So, we have a new plaster pool that I have been maintaining using the TFP method since about the middle of December 2022. Everything has gone fairly well so far. (Minus that I found out after the install was done that some of the equipment chosen by the PB was not the best.)

But I just noticed this week that I seem to be developing these spots on my pool that are very small brown/black dots all over the tanning ledge and then some of the same spots randomly throughout the pool.



Here are my last test results:
FC: 6
CC: 0
PH: 8.0 (lowered with MA)
TA: 90 (raised this over the weekend as it was sitting around 40)
CSI: .29
CH: 375
CYA: 45

The only noticeable thing with my levels is I am still adding MA pretty much daily to keep the PH down and then liquid chlorine as well. I have to add baking soda when MA reduces TA too much as well.

I have placed a chlorine puck on the spots and left them for 15 minutes and there was no noticeable change. I have tried some vitamin C tablets in a sock and rubbed/left them on the strain for about 15-30 seconds and couldn't notice a change.

From standing distance they are hard to notice so it's isn't too bad yet but I don't want it to get worse.

 

[douglasrlee]

Also, I did go to Leslie's when I first noticed to get my metals checked, because I've always been curious since I'm off of a well, but the iron was 0 and copper was 0.3.

 

[mknauss]

Welcome to the forum.
Any kind of granular fertilizer spread in the area?

 

[douglasrlee]

So, I do have a company that does my yard but the last application was a dyed spray pre-emergent a month ago ish. I did spray some weed and grass killer in the beds around the pool a couple of weeks ago. I don't know that that would do anything.

 

[mknauss]

Great. Any seeds, etc from trees? Just searching for what it could be. Not likely to be from the plaster.
Can they be scraped off?
They appear very similar to some recent posts from folks using a product called Milorganite fertilizer in their surrounding area.

 

[douglasrlee]

So, it has been very windy in Oklahoma here lately and I have been curious if something blew in from somewhere. I live quite a ways out in the country but it is still possible.

Do you know if there is a way to test/confirm if it is a stain from that fertilizer?

 

[douglasrlee]

I was initially under the impression that is black algae but the more and more I look at it, and the more and more I read, the less I believe that.

 

[douglasrlee]

And to answer your first question, no. No seeds that I am aware of, but being out in the country and with the wind it could be possible that something blew in.

 

[mknauss]

Do you know if there is a way to test/confirm if it is a stain from that fertilizer?

Typically iron is the issue with fertilizer. But the one I mentioned above does not seem to react to Vitamin C

I doubt it is black algae. Again, can you scrape one off?

 

[douglasrlee]

I've only tried to scrap it off with my fingernails and I can't get it off of the plaster that way. I have yet to try anything sharp for fear of hurting the plaster. I did notice at lunch today when emptying my cleaner that the plastic on the outside of the cleaner also had the same spots on it. They would scrap off though.

 

[mknauss]

Find a non noticeable area and use a putty knife or something to see what happens. If you are getting the same thing on the cleaner, it is likely something being blown in. If it is seeds or something else organic, chlorine will take care of it.

 

[douglasrlee]

So, would that be something that I should maintain chlorine levels and it'll go away type of thing or should I start rubbing tablets on the affected areas? I'll try the putty knife idea this afternoon.

 

[mknauss]

Hard to say. Least invasive is to leave them be and see what happens. If it is from the environment, it should stop once whatever it is has bloomed, etc.

 

[douglasrlee]

Ok, I just didn't want them to get worse or if it was some black algae or something to spread.

 

[douglasrlee]

But thank you for your help and quick responses! I will monitor it and see.

 

[mknauss]

Black Algae normally appears in grout lines, dead flow areas. And after extended periods of under chlorination.

No problem. Let us know what happens.

 

[douglasrlee]

Warmed up a little to get in today. I noticed the spots are mainly the tanning ledge and the corners around steps. Still think this is just something that was blown in?