Black (I think) Algae that will not go away

drewh

Well-known member
Oct 19, 2014
101
Brisbane, QLD, Australia
Thanks for all the input, so the strong consensus is that the higher chlorine isn't contributing to the surface changing. Could it be that it has cleared up the water more and thus I can notice the additional marks etc. very clearly? The pool water was NOT cloudy or murky at all before I started, so I'm not sure how much more it could be clarified by the chlorine (I had planned to use some of the remaining water clarifier I had after the SLAM). I've known where all the marks are very clearly and no question they look worse since Mon but as yours say that can't be the chlorine.

OCLT result was 1ppm loss overnight, so thats good. I'll keep the SLAM going until I can't see that dust & there isn't those early algae areas to brush away. But in any case it looks like I'm pretty close.

I'll do a full test this avo and post results. Appreciate everyone's ongoing help.
 

duraleigh

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Apr 1, 2007
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so the strong consensus is that the higher chlorine isn't contributing to the surface changing.
Drew, it's not a strong consensus.....it's factual.....chlorine does not contribute to plaster loss......period.

I would say once again you spinning your wheels by "hypothesizing" what might be going on in your pool rather than simply sitting down and reading and beginning to understand Pool School. Folks have been working on that technical info for years........it is correct.

You seem to want to draw your own conclusions which are incorrect and will only lead you down a path of failure. Nevertheless, that's your right to do that but it's hard to help you meaningfully when you alter the conclusions that are being given to you for free. Good luck with that pool......it IS looking much better.
 

drewh

Well-known member
Oct 19, 2014
101
Brisbane, QLD, Australia
Dave, that is not correct at all. I've always listened to the excellent advice here. Like I said, I followed the SLAM process down to a tee. I know my pool very well & know the marks which are hard to accurately convey via pictures. If I ask questions it's because I want to learn from people on here that really know their stuff, not question their judgement. I'm not sure what response from me would make you happy & feel that I'm not drawing my own conclusions - because I AM NOT. Every piece of advice I've been given I've listened to and followed. I think the worsening marblesheen has prob added a slight complexity to it all but still, that doesn't change the fact that I've listened to all advice & GREATLY appreciate everyone's time, and it's entirely because of that great help that the pool has cleared up really nicely.

Why always the caustic replies to posts? If you think I'm here to disagree with others and not listen, you are completely wrong.
 

zethacat

LifeTime Supporter
Could it be that it has cleared up the water more and thus I can notice the additional marks etc. very clearly?
Indeed. My water is so clear I can see every speck of quartz in the plaster. Of course, that means I can also see every imperfection as if there were a bullseye on it. Based on everything you've posted it sounds like maybe you had slightly cloudy water (due to algae) for a long enough time that maybe you started to believe it was normal(?)

I'm not sure what response from me would make you happy & feel that I'm not drawing my own conclusions - because I AM NOT. Every piece of advice I've been given I've listened to and followed.
You stopped SLAMing despite still seeing algae. If you don't complete the SLAM from start to finish, you may still continue to have algae and never experience the crystal clearness that you deserve to have. We want you to have a crystal clear trouble free pool as much as you do.
 

drewh

Well-known member
Oct 19, 2014
101
Brisbane, QLD, Australia
Indeed. My water is so clear I can see every speck of quartz in the plaster. Of course, that means I can also see every imperfection as if there were a bullseye on it. Based on everything you've posted it sounds like maybe you had slightly cloudy water (due to algae) for a long enough time that maybe you started to believe it was normal(?)
Yes that was prob the case - it wasn't 'cloudy' but maybe just enough to hide some of these other marks and the SLAM has brought that out, and maybe also the brushing as Jason suggested.

When you stated you stopped SLAMing despite still seeing algae, that means you were not following the instructions "to the t". If you don't complete the SLAM from start to finish, you may still continue to have algae and never experience the crystal clearness that you deserve. We want you to have a crystal clear trouble free pool as much as you do.
I'm sorry I worded it like that. My immediate reaction was to panic as I know the surface isn't the best (prob not bad for 20 years) so I should have ASKED if I should stop it or what people think (it was night anyway so I didn't stop anything as it's now morning and I'm continuing). My bad there. I'd also asked so many questions that I just tried to make an informed decision to limit the problem thinking people would be sick of all the questions (maybe that's what Dave didn't like, but the intention was NEVER to downplay or disregard the experts opinions on here). I think TFP is an amazing resource and the people like you and others make it so.

I hope to help others myself too as I learn more and more.

The pool is looking really good, def the SLAM is working wonders.
 

zethacat

LifeTime Supporter
You're fine man. I guess it was just a little odd that you were worried about high chlorine after "cal hypo bombing". I mean, shocking a pool is how you get rid of living stuff. It's a lot more likely your plaster corroded some during the period of time you were holding your PH at 7.0. I don't think lowering your PH has any sanitizing effects. Usually you lower your PH below 7.2 if you want to do an acid bath -- in other words, willingly corrode your plaster to get rid of stains or calcium buildup. Not sure whether something like that is even recommended for 20 year old plaster.
 

drewh

Well-known member
Oct 19, 2014
101
Brisbane, QLD, Australia
Hey zetha, I hear you. The cal hypo bombing was just based off what my late father would do etc, he didn't really get into the details of what effects different chemicals had etc, would usually use cal hypo and broadcast it over the pool as that's what 'everyone' here at the time did, and so I followed suit. But not for the last 10 years prob, I mentioned that just as wondering if the chlorine hitting the green algae (different algae, different situation & different thread to this one) had a quicker killing effect than the liquid chlorine having to spread around the water & then kill it. Also re pH lower, this is what I was told by the pool shop & what I read online in multiple places, that lowering it into low 7s (7.2) would soften the waxy coating on the black algae (remembering I thought those two marks were black spot) etc etc. pH would have rarely got to 7.2 and no lower as I did read about it being too acidic below this & damage to plaster.

With this, I just felt that areas had deteriorated especially as I was looking at them almost daily in detail - I could take pics to show this. But it's prob more what Jason said that the extra brushing might have been enough to just loosen more slightly.

Anyway, I'm still slamming and will continue until I no longer see that slight beginnings of the algae & no more dust when brushing it away. The OCLT passed yesterday and CC's are 0, so I'm pretty close I think.

Been a great journey and I've learnt a stack. The pool is also looking fantastic - thanks to all!
 

zethacat

LifeTime Supporter
You can use pool math to see what the effect of adding cal hypo is but basically it's just chlorine with calcium chloride added (to increase your calcium hardness). Granular products need time to dissolve whereas liquid products are effective instantly.. so it's somewhat backwards to think that granular chlorine would have a faster sanitizing effect than liquid chlorine.

By the way, it's borderline blasphemy on this site to say "the pool store told me". Think of this forum and the pool store as your girlfriends and the time has now come to choose which one to be with. :D Once you choose, you don't talk about the "other woman".
 

drewh

Well-known member
Oct 19, 2014
101
Brisbane, QLD, Australia
Yes true re cal hypo it was just a question asked for that other issue ages ago but I was way off! Not relevant to this SLAM now anyway.

Haha... I learn that within a few msgs re pool store, and needless to say I haven't been there since started reading TFP and have no intentions to ever again! So I've picked TFP as my girl of choice ;) I don't think I did mention it after those first few posts so I hope I was a quick learner!!

Having lots of rain here today owise would do the full test results, I will as soon as it clears up.
 

drewh

Well-known member
Oct 19, 2014
101
Brisbane, QLD, Australia
Re: Black (I think?) Algae that will not go away - any help appreciated!

Ok test results are:

FC 12
CC less than 0.5
pH 7.8
CH 300 (of all four tests done with TF100 every one has been different, last result 2 weeks ago was 225 - and each time I've done the test twice immediately afterwards to check I get the identical number. Any idea why it's jumped to 300? Would this have anything to do with the surface issue or not at all?)
TA 130
CYA 20

There is still algae (that's black in colour) forming - what I'm noticing is almost all of these areas are spots where pitting has occurred / the surface is weaker/rough.

Also I've mentioned it before but the colour of the algae (a black colour) is identical to the colour of the surface under the marblesheen (as I know when I mistakenly scrubbed a part away). Could this mean anything?

Greatly appreciate everyone's ongoing help with this.
 

zethacat

LifeTime Supporter
Keep slamming until there is no visible algae left. Once you get rid of it should not come back as long as you maintain the proper level of chlorine moving forward. Sometimes I have to re-do my CH test.. yesterday it was 300 and when I re-checked it came to 250. If the drops come out too fast or inconsistent you will not get consistent results. Let the drops form at the tip of the dropper as slowly as possible and fall off naturally. It gets tougher to do when there isn't much left in the bottle.
 

drewh

Well-known member
Oct 19, 2014
101
Brisbane, QLD, Australia
Re: Black (I think?) Algae that will not go away - any help appreciated!

Thanks zetha will do, keeping at it!

Re CH test, each time I've done it a second time immediately after and got the same result, on the same drop changing colour. So the results themselves are valid. But anyway just wondered that's all.
 

drewh

Well-known member
Oct 19, 2014
101
Brisbane, QLD, Australia
Re: Black (I think?) Algae that will not go away - any help appreciated!

Hmm I wondered about that re corroding plaster.... Hope that isn't a really bad sign.

Re cal hypo, forget I ever mentioned it? I haven't used cal hypo for 8-9+ years. I only asked in a diff thread just regarding a diff issue for people's thoughts. Don't even have any cal hypo here, only liquid chlorine and salt :)
 

zethacat

LifeTime Supporter
Unless you were meticulously maintaining the plaster since it was new, 20 years doesn't sound so bad. I think you should realistically expect to have to re-plaster sometime within the next few years depending on your tolerance for the way it looks or how much more falls off, but that is just an educated guess (taking into consideration my education on the subject is very little to begin with). I'd be curious to see what it looks like when the algae is completely gone, and the pool is nice and clean and the water is crystal clear. Only then could I even given an opinion on whether I would re-plaster it if it were my own pool.

I think we already know Jasons opinion :laughblue:

Bottom line, your pool surface is shot and clearly needs to be replaced.
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
Chlorine will oxidize ammonia and nitrogenous (and some other) organics or combine with such organics, but plaster surfaces do not contain any such substances and do not react with chlorine. Marblesheen is a mixture of white cement and crushed marble where marble is mostly calcite (calcium carbonate) or dolomite (calcium magnesium carbonate) that again chlorine does not attack.

It's most likely that the plaster and marble surfaces have degraded over the years, possibly accelerated in such degradation by not maintaining water saturation with calcium carbonate (i.e. CSI near zero) though as others have noted 20 years would be a decent run for a plaster pool (and Marblesheen is not the same as PebbleSheen® or PebbleTec® since marble is much more like plaster that can dissolve whereas the rocks used in the latter have more silica). Such degradation creates pitting and wear of calcium carbonate and then algae can grow in such surfaces. If such wear was so great that such algae was holding some of the surface together almost like a glue, then chlorine killing the algae and oxidizing some of it to break it down (along with brushing if you were doing that) could cause the surface to degrade more. That is not a direct result of the chlorine, but an indirect one in terms of killing and removing algae that may be embedded in the pool's surface.

If the plaster is degrading, then you may find the pH, TA and CH all rising as a result if calcium carbonate is dissolving into the water (if calcium hydroxide were getting converted into calcium carbonate in place, then the pH would rise but the TA and CH would not). That would generally mean that the water was not saturated with calcium carbonate (i.e. the CSI not near zero). As noted in numerous links when one searches for Marblesheen (this one and this one for example), Marblesheen seems to have a reputation of degrading in a way that algae forms and penetrates deeply and where companies sell paint to resurface (we're not recommending that -- paint has its own issues generally not lasting that long).

If the main reason you were having a negative CSI was to reduce calcium carbonate scaling in the SWG, then using a non-carbonate pH buffer such as 50 ppm Borates would cut down the pH rise at such plates in half so that your CSI should not need to be as negative.
 

drewh

Well-known member
Oct 19, 2014
101
Brisbane, QLD, Australia
Chemgeek thank you for the super helpful reply - very interesting to read it all & learn.

Here in Australia in the early 90s, at least in Queensland, many, many pools were Marblesheen (can think of about 10 in these few streets). I think you're spot on re the algae getting deep into the surface especially where pitted - I've noticed that maybe 85% of the algae would form there, with the other parts on actual smooth marblesheen.

The algae that formed in the smooth part has completely gone and I can't see any more forming in the pitted/rougher areas. Part of the problem is more of the black surface underneath is starting to show through.... is this the concrete below the Marblesheen layer? See these pics (it's quite a bit worse than pics show):





I did an OCLT last night and it was 0.5ppm overnight loss. I will do another tonight to confirm. CC has been 0-0.5 all the way through. So per the article, I'm good to finish the SLAM?

Chemgeek - I'll definitely add the 50ppm borates to the pool asap per the article, thanks for explaining that. Anything I can to help minimise the surface deterioration. I don't have the funds to resurface (Vinyl liners here cost 5-6K minimum) but that will obviously be the next step.

Going forward, what would people think I should keep the CSI at? I do get a lot of buildup of calcium on the SWG plates (Jason told me to keep the pH lower to help with this), and the borates too would help.

Current test results are:

FC 12
CC < 0.5
pH 7.8
TA 130
CH 300
CYA

Going forward, should I raise the CYA to 60 as per the Chlorine/CYA chart? Maybe in a step to 40 and then 60 as Pool School recommends with adding chemicals/CYA?

Thanks to all.
 

zethacat

LifeTime Supporter
Sounds like you're done SLAMing as long as your water is crystal clear and you're positive you don't see even the smallest amount of algae. A CSI range of -0.3 to +0.3 is normal. As long as you maintain the proper levels of chlorine and keep your CSI within that range, you should be fine going forward. I think at this point re-plastering would just be a personal preference. The disadvantages of pitting are mainly aesthetics and roughness, but you must be diligent on maintaining that proper level of chlorine as there are a lot of places for algae to hide.
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
The surface underneath the Marblesheen may be gunite but that won't be black though it usually does look darker than white plaster (it's usually gray). If it's black, then maybe the black algae went all the way through to that layer. Gunite (shotcrete) is just another form of cement and sand mix rougher than plaster, but since it has cement it too needs to be protected from degradation by having the water saturated with calcium carbonate.

With proper chlorine levels and decent circulation, you should not normally have black algae but with the severe pitting in parts of your plaster it will be hard to get chlorine in those crevices all the time so some algae may persist though the SLAM has gotten rid of a lot of it.

As for the CYA level, that depends on how much chlorine you normally lose and the size of your saltwater chlorine generator. We usually recommend 60-80 ppm usually with 80 ppm preferred for SWG pools because most units are woefully undersized so need all the help they can get in terms of protecting chlorine from breakdown from sunlight and minimizing chlorine usage also lowers the rate of pH rise since the SWG won't be on as long.
 

drewh

Well-known member
Oct 19, 2014
101
Brisbane, QLD, Australia
Zethacat - thanks for the info. I think I'm done now, OCLT again 0.5ppm and it's looking clear. I've looked as close as I can into the pitted areas and it looks like the algae has gone (some are hard to tell because I can see the gunite/surface below it which has been a very similar colour to the algae.

The surface underneath the Marblesheen may be gunite but that won't be black though it usually does look darker than white plaster (it's usually gray).
Thanks chemgeek really interesting to read your reply again. Spot on it is a dark grey colour. Seems like the Marblesheen surface thickness varies quite a bit, on the walls it looks 5-7mm (one spot had cracked off so I could feel the depth) whereas on the floor near the edge it's very thin maybe 2-3mm?).

If some algae reappears after I'm done SLAMing, what's my best approach to tackle it again? As far as I can tell I can't see any remaining but it wouldn't surprise me if some is deeply in there & in crevices etc.

Thanks re CYA, I'll take it to 60 and then measure what sort of FC level the SWG is maintaining and go from there, making sure I'm never under the minimum 3 as per the chart.

What would you recommend as a CSI target for the pool given all the plaster issues etc (zethacat mentioned the -0.3 to 0.3)? Could I aim for very slightly negative to help with the buildup on the plates (I'll add the borates in the coming months) or should I keep it slightly positive?