Advice needed to diagnose / remove spotting

[gustafson]

I've had a difficult spring with the pool after it turned green during an unanticipated 4-week trip out of town, and again for a week when the motor broke down while I was SLAMing my way out of the situation. While in the past I've mainly had algae growth on the walls, this time the pool floor got hit with algae, leaving numerous dark spots after the customary brushing. I've been spending the last few days elevating the chlorine levels, but my plastic brush wasn't getting the spots off, so I ultimately caved in and started using a metal brush to gently scratch off the algae, which is taking forever. Just wondering if others have encountered this issue and how best to deal with it.

My feeling is the spotting is due to pitting in the plaster, and I'm wondering if this calls for replacing the plaster - a cost I'm looking to defer if possible. Alternatively, I wonder if I'm being too paranoid and it's OK to aggressively brush the spots off until they're gone.

Finally, I'm wondering if there are other methods to get the spots out. I found with the metal brush that it works better angled when the edges scrape against the spots, which made me wonder if using a toothbrush would work better, or a small brush head that could be attached to a part of ones foot (say the big toe) to target these spots better.

Thanks in advance!

 

[pooldv]

So, have you successfully completed the SLAM now? And brushing during the SLAM didn't clear it up? It is ok to brush it with a stainless steel brush.

It could be black algae. More here, Pool School - Black Algae

 

[gustafson]

So, have you successfully completed the SLAM now? And brushing during the SLAM didn't clear it up? It is ok to brush it with a stainless steel brush.

It could be black algae. More here, Pool School - Black Algae

Thanks for the advice. Turns out it is indeed black algae. I got one of the clumps that broke loose after brushing, and it left a dark green smear. Boy, this stuff is a nightmare.

As for SLAMing, I ran out of reagents recently and am waiting for refills to come in, so cannot confirm as yet. But I've been maintaining sufficient chlorine levels by adding a gallon or two of chlorine daily. Will be able to confirm once my reagents come in.

On a related note, are there any typical conditions or markers that indicate rapid loss of plaster? Or contrarily, are there simple guidelines to follow to ensure minimal loss of plaster? Thank you!

 

[Mr Bruce]

If you fill out the Pool Calculator with all your numbers (including temperature), it will tell you your Calcite Saturation Index. The happy spot is slightly negative. Anything lower than -0.6 means your plaster may have a shorter life. Not everyone feels the need to manage CSI religiously, but I do think it a good idea to at least play with the numbers one time and get an idea of what matters the most (CH, temperature, etc) and how they affect +/-

 

[pooldv]

Agreed, paying attention to your CSI will definitely not make your pool worse.

More about etching here, Pool School - Calcium Scaling

You can defer replastering as long as the pool isn't leaking. Once it leaks more than you can fix it then replastering moves up on the to do list. Otherwise, it is just cosmetics.