Is this black algae??? Or something else due to the plaster defects....

[speedwater]

Need a second opinion....does this look like black algae to you guys or some other kind of oxidation/reaction? The touch is slightly slippery but not overly slimy.

I'm a fairly new pool owner (Oct 2017). I successfully fought a green algae issue in January using the SLAM but now I have what looks to me to possibly be black algae forming only where there are issues with the plaster (old pool, needs to be re-plastered). Whatever this is is virtually impossible to brush off. Regular pool brush is worthless. I've swam down with a hand brush and it was completely ineffective as well. I can't even really scrape it off with a fingernail. It hasn't appeared on all of my plaster defects YET but does seem to be very slowly increasing. If I can find something that is effective at lifting it then I'll probably go rent a scuba tank and get after it. It is nowhere else in the pool...no corners, nowhere on the steps, etc. It's only present on the plaster defects...mostly at the edges inside where it has chipped away.

I've been following the TFP methods using liquid chlorine, testing very regularly, understand and have performed the SLAM, etc.

Current numbers:
FC - 5
TC - 5.2
ph - 7.6
TA - 86 (just made an addition to bump it up some more to get it 90+)
CH - 275
CYA - 32
Borate - 50

Thanks,

Mitch

 

[kcindc]

CYA results are always rounded up, so a result of 32 should be rounded up to 40.

The photo you posted almost looks like looking a sample under a microscope. Can you take another photo that isn't so zoomed in?

Have you used an algae brush on it? Do you have a stainless steel algae brush like this one? https://www.amazon.com/Milliard-Designed-Concrete-Walkways-Extremely/dp/B00IT2W22A/ref=sr_1_4?ie=UTF8&qid=1500401045&sr=8-4&keywords=algae+brush

It might help if you can scrape some off and rub it on a paper towel. Black algae will look greenish on the paper towel.

No reason to change your TA unless your PH is swinging up/down. Aeration increases PH and doesn't impact TA.

 

[speedwater]

After some more reading on the 'net I think it is what I think it is... Going to order a stainless brush (no I don't have one) and also read a suggestion to rub a chlorine puck on the spot. I'll try that as well.

There was a little greenish to it when I last swam down to look closely.

I do have some PH swing...it keeps running up to 7.8 and I keep adding some acid to bring it back down...about every 2days I'm having to add acid. Although that may just be due to aeration.

 

[kcindc]

I do have some PH swing...it keeps running up to 7.8 and I keep adding some acid to bring it back down...about every 2days I'm having to add acid. Although that may just be due to aeration.

View attachment 66069

If you have a PH swing, there is no need to "bump" your TA. The higher your TA, the faster your PH will rise. There is no need to aerate unless you are trying to reduce your TA or you have water features that aerate the water.

A couple of ideas of the staining.

1) you need an algae brush for a plaster pool, so order it anyway and use it.
2) to test a stain you can try to things:
a) put a puck on the stain for a few minutes, if the stain lightens the stain is organic (like algae or leaves, etc).
b) if the puck doesn't lighten the stain, crush some vitamin c pills and put it on the stain for a few minutes, if the stain lightens, the problem is metals.

 

[speedwater]

I was mistaken about aeration. I have none. Thanks for the tips, I'll give the pucks and C a try...I'm betting it's organic. I've got an algae brush on the way.