Black algae, metal deposit or other?!

[vmatki]

First post! Hello everyone :-D

Until this week I had an easy pool, very stable and crystal clear with gleaming white plaster walls. I was testing every other day and kept everything fairly consistently within the recommended ranges.

On Monday I noticed the Cl was low – almost zero. In the aftermath of some heavy use and rain I wasn’t surprised: it was due a pool shock. Whilst shocking I noticed the beginnings – fewer than ten 1" circles – of green/yellow algae on the walls. I scrubbed them away – and brushed my entire pool – as well as pool-shocking and brushing for the next 3 days straight. The yellow/green algae patches disappeared. The water was crystal clear (it never wasn't). The Cl (TC & FC) held its ppm nicely.

But yesterday (Thursday) and today even more so I noticed:
- grey/blue/brown speckles on areas that are prone to poor circulation and gathering organic matter (e.g. steps and benches)
- larger areas of the walls and floor that look less than bright white (greyish), especially in low light
These markings only emerged in the aftermath of the super-chlorination. None of them brushes off.

Factors to consider:
- I found out today the phosphate level is very high (2500ppb). This come as a shock, since we do our own gardening, the pool was only filled in April and we haven’t been near it with fertilisers or mulch. The only organic matter to have entered the pool is palm flowers (‘tis the season!).
- Historically, I had been keeping my Cl at the low end of the recommended range on the recommendation of the pool builder because I have an ozone-generator…
- The temperature these past couple of weeks has shot up to the 90s/100s (I’m in Houston).
- The chemistry (apart from phosphates) is otherwise fine. Cl slightly too high now on purpose. CH slightly low but will get to that after phosphates. pH within range to let the chemicals do their job….

First things first, I must rid my pool of the phosphates (beginning now). In a day or two, I need to tackle the speckling and greying issues.

But the question is, am I dealing with (duh duh duuuuuh!) black algae or is it some consequence of super-chlorinating so intensively (a metal or calcium deposit)? Or something else altogether (plaster)?

Photo below of the speckles. Tiles are 3”x3”, to give you a sense of scale.

THANK YOU in advance

 

[Donldson]

Welcome to TFP!

Ok, I am going to jump right in to it. First thing: forget everything you have been taught about phosphates. It is a completely needless measurement that pool stores use to sell phosphate remover (quite a good profit margin on that stuff). If you are in the process of adding phosphate remover you can stop right away and if you have any you can return you should do that. I promise, once you learn some more you will understand that it is completely unneeded in a properly chlorinated pool. So is regular shocking in fact.

Ok, do you look like this yet ? Good, that means you are ready!

Post your full test results please. FC, CC, pH, TA, CH, and most importantly CYA (or stabilizer or conditioner, whichever the pool store calls it). You are going to be told that pool store results are inaccurate, and they are but let's see what you are basing your work on. We also need to know the size of your pool, what type of filter, and your chlorine source. All of this information will help us help you figure out the source of the specks.

Next, click the pool school link in the upper right corner and start reading. Find a few articles that may interest you but try to read as much as you can. You are in the right place to get your pool in good shape but it is going to take some reading and learning.

 

[BoDarville]

Welcome to TFP!

First things first, I must rid my pool of the phosphates (beginning now).

You can ignore the phosphates. There are some members with phosphates levels of around 5,000 and never get algae because they keep their chlorine level within the range for their CYA.

That's a good lead-in to the real culprit: low chlorine levels - ozone generator or no ozone generator.

To test for black algae, take a sample and smear it on white paper. If it smears dark green, it's probably black algae. To see if it is a metal stain, take a vitamin C tablet and hold it on the stain for about a minute while rubbing it gently. If the stain lifts, then it is a metal stain. Sometimes, superchlorinating can cause any metals present in the water to form stains on surfaces.

Now, back to the chlorine. To determine the target chlorine range, you need to know your CYA. If you do not have a way to test CYA, I would get a Recommended Test Kit right away. BTW, don't assume you can trust pool store water testing as it is often inaccurate, especially for CYA.

If you do have a test kit (even if it's not one of the recommended ones), please post whatever test results you can to give us a more complete picture.

 

[Richard320]

Welcome!

First off, phosphates don't matter, except to the pool store bottom line. Stop throwing money away. What you've probably just spent on that snake oil could have bought you a lot of useful stuff. Scroll down in this thread and read Chemgeek's explanation.

"High" and "Fine" and "slightly low" tell us nothing as far as the pool chemistry. What you think might be slightly low chlorine could be so low as to be useless, depending on your stabilizer level. Or the stabilizer itself could be too low if the pool was seriously diluted with rain, in which case the sun is getting to the chlorine before it can get to the algae. What we need are objective results - numbers.

The spots could well be black algae. That requires high FC levels and elbow grease.

The cure begins with a decent test kit, decent being explained in the article in pool school, and some understanding of basic pool chemistry.

We'll walk you through it, but since none of us are there with our test kit, you'll have to get the results for us. Pool store tests don't count.Here's an example of why not.

 

[vmatki]

Wow! Replies already. Thank you. I’ve learned so much just from your three answers.

Phew. I haven’t jumped in with the PhosFree quite yet. I was upsold it the first time I visited a pool supply store with a test sample, but I hung tight on the instinct that my (at the time) brand new pool shouldn’t require such drastic action.

I’m naturally circumspect so make a habit of taking two samples to two pool supply stores and comparing them with my own. I also run two test types of my own (Aquachek 7 test strip and Pentair drops). Paranoid or what.

The results are:

Pool Store A / Pool Store B* / My Reading A (strips) / My Reading B (drops)

TC: 3 / 5 / 4 / 3+ **
FC: 3 / 5 / 4 / no test
pH: 7.5 / 7 / 7.2 / 7.2
CH: 150 / 150 / 200 / no test
TA: 80 / 60 / 80 / 90 / 90
CYA: 45 / 90 / 30-50 / no test
TDS: 500 / 600 / no test / no test
Copper: 0.3 / 0 / no test / no test
Iron: 0 / 0 / no test / no test
Phosphates: 2500 / 2500 / no test / no test

* The data for this sample (I just noticed) is based on the wrong volume: they used 15,600 gallons instead of 10,600…not sure how this affects results.
** This is higher than I had been keeping it; on advice (possibly erroneous, due to upselling of ozone generator!?) I was keeping Cl nearer 1ppm.

About my pool:

Size: 10,600 gallons
Filter: cartridge
Sanitizer: trichlor tablets (99%, in line), pool shock as required with calcium hyperchlorite granules (68%) or sodium hyperchlorite (liquid bleach 9%)

@Donldson Thank you. Results above. Yes, I will read read read!

@BoDarville I tried rubbing the marks with a lemon (as per advice I picked up elsewhere on here) and they didn’t lift. I will obtain some Vitamin C tablets and get back to you. The specks are dry (no slime - yet?!) and completely bonded with the plaster surface, so I can’t remove any to smear on some paper and check the colour. The algae blooms from earlier in the week were yellowy green, but they brushed off easily and haven’t returned. These specks appear (against the white plaster) to range from blue to grey to dark brown. On the plastic returns there is some black. Thank you for your suggestions. Let me check with the Vitamin C tablet, which is probably a bit more precise and potent than the lemon.

@Richard320 You would think I would know being the daughter of a Chemistry Teacher…I think I thought you could diagnose my specks on an image alone (I am an Art Historian after all!). Anyway, results above. I am learning something. Thanks!!

 

[Richard320]

Hmmm... That's quite a spread there on that CYA. So which is it?

Sadly, the effective free chlorine level is dependent upon the CYA level. We're no better off now than we were before. Your FC could either be fair or too low to be of any use.

 

[JamesW]

It might be copper. Ozone is particularly good at oxidizing metals.

The black on the plastic returns is a good sign of copper staining. The ozone oxidizes the copper and the oxidized metal plates out on the returns.

Do you have a heater, or have you used copper based algaecides?

 

[vmatki]

@JamesW No heater, no copper based algaecides. Only abnormalities in the last week have been a drop to zero FC and then my self-prescribed treatment of 3 days of FC at 10-20. There are black deposits on the ozone return, but they do seem mould-like in texture.

@Richard320 Do you think I should take another sample to another store tomorrow and test for CYA again!? It’s been showing as 30-50 on my Aquachek strip for the last 3 months and hasn’t gone up or down. Perhaps that’s the one we believe?

Thanks guys. I really do appreciate your input.

 

[Donldson]

CYA: 45 / 90 / 30-50 / no test

And this is why we don't like pool store results, or test strips. One store is definitely wrong, the other may be wrong, but we don't know if one is right or not. As for your test strips, what if your car speedometer showed your speed as "30-50"? Not very helpful unfortunately. That's why we really only recommend two test kits, the TF-100 (I use and love it) and the K-2006. All the tests you need, including one called FAS-DPD which gives you very accurate chlorine readings. Non-existent in most kits.

Richard is right, the CYA is most important. This Chart shows why you need to know it, and why you need to be able to read chlorine levels higher than the OTO drops and more accurately than test strips.

Truthfully we aren't going to fully believe any pool store results (see why above). As for the test strips, we need to know if it's 30, 40, or 50? Or is it just plain wrong?

 

[vmatki]

@Donldson Thanks so much for the link to the CYA-FC chart. I had no idea there was such a variance in the FC target depending on CYA levels. I thought I just needed to get both within their respective target ranges.

So, if CYA between 30-100ppm is theoretically "acceptable", are pools in the upper levels really chlorinated to between 7 and 12 ppm? I feel like this is contrary to what I have been told is “safe” for swimming (i.e. FC under 5ppm). I was also told to be sure not to ever over-stabilise, which would result in having to drain the pool and start over.

Anyway, it’s clear that I need to get myself a more accurate kit so that I can find out my CYA and target FC (thanks for the TF-100 tip). Say for argument’s sake that my CYA is around 40, and my FC has been around 1ppm for 3 months, I have been under-chlorinating by between 2 and 4 ppm this whole time…

…which leads me further to the algae conclusion. Although, again, perfectly clear water and no slime this whole time. Just these little specks in the last week of increased chlorination!?

So there can be no harm, can there, from pool shocking again tonight? I just don't want any more "algae" growth while I'm getting all this figured out.

Will get back to you with an accurate CYA.

THANK YOU! I’m going to go and have a beer now that I’ve been let off PhosFree duty

 

[Donldson]

So, if CYA between 30-100ppm is theoretically "acceptable", are pools in the upper levels really chlorinated to between 7 and 12 ppm? I feel like this is contrary to what I have been told is “safe” for swimming (i.e. FC under 5ppm). I was also told to be sure not to ever over-stabilise, which would result in having to drain the pool and start over.

CYA should typically be between 30-50 (except for salt water pools, but that is another topic). This is enough to protect the chlorine from significant degredation from the sun while not being over stabilized. As it goes higher levels become somewhat crazy. The "safe" number is considering absolutely no CYA, it is an old rule of thumb that just won't go away even though almost all pools have some CYA in them now. I consistently maintain 4-8 ppm chlorine and people think I don't use chlorine since their eyes don't burn and they can't really smell it.

Anyway, it’s clear that I need to get myself a more accurate kit so that I can find out my CYA and target FC (thanks for the TF-100 tip). Say for argument’s sake that my CYA is around 40, and my FC has been around 1ppm for 3 months, I have been under-chlorinating by between 2 and 4 ppm this whole time…

…which leads me further to the algae conclusion. Although, again, perfectly clear water and no slime this whole time. Just these little specks in the last week of increased chlorination!?

Perfectly clear water is a good sign, but not a very strong one. Algae, along with other nasty stuff, can exist in an underchlorinated pool. Slime is not a problem in a properly chlorinated pool. It could well be algae, though I really cannot tell from the pictures.

So there can be no harm, can there, from pool shocking again tonight? I just don't want any more "algae" growth while I'm getting all this figured out.

Next article to read is how to SLAM. Traditional shocking is almost always inadequate to take care of the problems and get everything out of the water. The SLAM process is designed to make sure everything is out of the water before you consider the job done. Once this is done and proper chlorine levels are kept the pool starts to become truly Trouble Free!

So look in to that, and enjoy your beer

 

[vmatki]

My TF100 test kit has arrived. Here are my updated results:

TC: 3.5
FC: 3.5
pH: 7.5
CH: 400*
TA: 80**
CYA: 45

* The CH test only worked when I added the reagents in the sequence required for having copper in the water (which the Pool Store suggested I did – 0.3ppm – although I have since added the treatment dose of MetalFree). Testing the normal way “faded to purple” at about 550, which I understand is an invalid result.

** This is now 130...rookie error, I overshot my target by added the "pool calculator" amount in its entirety.

My thoughts:

CYA at 45 says I have been light on the FC since the beginning, but CC of 0 says I don’t have an aggressive algae problem as things stand. Holding a trichlor tablet to the surface has no effect. Sustained high levels of FC and vigorous brushing (stainless steel) has no effect.

I performed Jack’s Magic stain ID tests and none of the included stain removers – iron, cobalt, copper – had any effect.

I would like to update my observations of the marks/stains:
- numerous pinprick indentations in the plaster filled with dark-coloured matter throughout the horizontal surfaces of the entire pool
- blueish spots that seem inherent in the plaster (underneath the surface?) and are throughout the walls and floors
- dark brown rice grain shaped flecks on the edges of steps and benches
- larger (2”) greyish smudges on floors

Again, all this appeared in the aftermath of repeated pool-shocking (to treat the original green algae circles on the walls, which have not returned). This is a new pool (3 months).


Questions:

Could the plaster be eroding (pitting?) and organic matter filling these pinprick holes? I have never let my CSI slip outside the acceptable range. (NB I have never needed to add Calcium Plus: brushing the loose plaster as it cured and smoothed out has always been adequate to keep it at the low end of the acceptable range. pH has never been too low and TA has never been lower than 80.)

Why did the CH more than double between the Pool Store test on Friday and mine 5 days later? (I haven’t added anything: only bleach, trichlor and baking soda to up my TA.) Is my test likely to be valid?

Could the 0.3ppm copper identified in the water have precipitated on the surfaces so extensively in the aftermath of the pool-shocking? If so, why would the Jack’s Magic stain test fail? Should I try a copper stain removal treatment? (I have no heater therefore I'm eligible.)

Could I still have an algae problem even though my CC is 0 and my FC is slow to drop?

Could there be something wrong with the plaster itself?

Would more photos help you to help me?!

Many, many thanks in anticipation.


Sleepless in Houston

 

[Donldson]

I'm going to try to hit on everything I can, there is a lot here. First, your CH levels are different for exactly the reason we tell people to get the kit: pool store results are a joke. If you followed the directions (and all signs point to you did) then it is a valid result.

You put TC and FC, but a FAS-DPD doesn't test for TC. After you tested your FC, you added the R-0003, did it stay completely clear? If so then we just ask that you write it as FC 3.5 and CC 0. This avoids confusion. Also you can have algae without CC, CC indicates a problem but it's absence does not rule out problems. If your FC has been lower than the stated minimum for your CYA then you should perform an OCLT to either confirm or rule out algae.

I'm going to let others tackle the stains and plaster, I don't have any first hand experience with either. You are on the right track and doing your own testing is going to keep you there. Keep at it!

 

[vmatki]

Thank you @Donldson and my apologies for the confusion with TC. Anyway, last night I was FC 3.5, CC 0. This morning I am the same. I guess I have passed the OCLT. Maybe we can rule out algae in the above considerations?

This being the case, do I need to start a new thread, knowing what I now know, in a more relevant section?

 

[duraleigh]

No, keep your info here...it helps to have continuity.

 

[vmatki]

3-month-old white plaster starting to discolor

Merged by moderator. I went ahead and combined these to avoid duplication. jblizzle

My three-month-old white pool plaster has started looking less uniform “white” than it did at first. Specifically, the entire surface is showing various grey, black and blue dots (pin prick sized) which together give a mottled/dirty appearance. In bright sun this is barely noticeable, but in low light it looks quite bad. They are definitely inherent in the plaster, whatever they are, rather than raised up.

Photographs don’t show much, but attached is one with enhancement to show the “dots” in their various colors to scale (one tile = 3”x3”).

Members here were very informative and helped me rule out algae and metals (see this thread: http://www.troublefreepool.com/black-algae-metal-deposit-or-other-t67234.html).

My pool builder/plasterer says it is normal discoloration, with the exception of a couple of spots where there is evidently some contamination (dirt/debris) trapped near the surface of the plaster that he says he will come back to “smooth” out.

My chemistry doesn’t really point to scaling, etching or pitting. The only thing I could be guilty of is perhaps a lack of brushing of late, although I run my robotic cleaner daily for three hours and brushed/vacuumed religiously during the first month as instructed.

Question: Is the pool builder correct, is this normally what happens as the surface of the plaster ages over the first three months and beyond?

Full chem:

FC: 4
CC: 0
pH: 7.6
CH: 350*
TA: 100**
CYA: 45
Copper: 0.3 (treated with MetalFree)
Phosphates: 2500+ (you people told me not to bother with PhosFree!)

*Pool store results have always shown CH to be 150-180, but my own careful testing has contradicted this. I have not yet had to add Calcium Chloride – the water seems to have had enough with the plaster dust that came off after filling.

**In the last three months this was maintained at 80-90. I recently upped it to be on the safe side.

Thank you kindly!

 

[karmabiker]

Re: 3-month-old white plaster starting to discolor

That does not look normal. ... interested to see what the other members have to say.

 

[JasonLion]

Re: 3-month-old white plaster starting to discolor

Copper at 0.3 is right at the edge of causing problems. It wouldn't be too difficult for high PH to cause copper stains. That said, your description and photo don't completely match with metal stains.

By the by, metal Free is not one of the recommended sequestrants. Sequestrants based on HEDP, phosphonic acid, or phosphonic acid derivatives are far more effective. ProTeam's Metal Magic and Jack's Magic The Pink Stuff (regular), The Blue Stuff (fresh plaster), and The Purple Stuff (salt) are some of the top sequestrants. You can also find many other brands with similar active ingredients, some of which are noticeably less expensive.

 

[onBalance]

Vmatki,
Based on the picture above (and pictures PM to me), the dark specks are not algae, and they are not metal stains.
Dark or gray specks can be from the aggregate that plaster contains. There are always some dark colored sand grains (among the dominate white) that will soon show up after plastering. That is normal and not considered defective.

Also, if dirt, leaves, and other organic debris blew into the pool while plastering, then they can be troweled into the plaster surface and will show as specks or even larger spots. Those (discolored) spots can be removed and will leave a slight avoid or indention.

If there are some rough areas, it is not from etching or pitting due to bad water chemistry. Your water balance is good, and would not cause etching in just three short months. Also, etching would occur uniformly across all of the plaster surface.
Allow your plasterer to return and sand (with sandpaper) any rough areas, along with removing some of the embedded dirt and organic debris etc.

 

[vmatki]

I deleted the basically duplicate post after merging topics and also removed the reference to the other thread below. jblizzle

Thank you onBalance for so carefully reading through my PM and for tying it back to this thread.

Your holistic view of the various factors is pointing towards a conclusion of:
(a) natural color variance in the aggregate of the plaster
(b) some rougher bits of plastering as a result of uneven troweling
(c) the entrapment of some organic matter during plastering

I can learn to live with (a) knowing that it is normal. And thankfully we have a pool builder who is happy to take care of (b) and (c) as well as he can. Best of all, I feel I can let myself off the hook for having caused these issues in the first place. Between this forum and my TF100 test kit (yay duraleigh!) I feel empowered to look after my pool with knowledge, awareness and the backing of a friendly and impartial group of pool enthusiasts.

Great work, TFP! Thank you thank you thank you!

vmatki :-D