Black (I think) Algae that will not go away

drewh

Well-known member
Oct 19, 2014
101
Brisbane, QLD, Australia
High pH coupled with high CH can quickly scale up the cell. Keep the pH lower and the problem should reduce.
Thanks I'll do that... will try keeping it in the lower 7's - do you / anyone ever/often use a pH buffer? I noticed no mention of it in the Recommended Pool Chemicals listing on the Pool School pages.

If you are able to scrape off some of the black spot and then smear it on a white piece of paper, if it's green (or dark green), then that is black algae. If not, then it may be something else such as an organic stain. If it doesn't scrape off, it may be a metal stain.
I tried doing that this afternoon - the problem is the only spots I can try this are the shallow and deep end steps. When I try to lift some of it, it just blows away like powder (literally that consistency). The actual algae (if its that!) in the middle of the pool, theres no way even getting into the pool I can easily take a sample of it (tried using the pool net but again it just gets pushed away/falls through it, though its definitely a tighter consistency). The other wider patches are again quite a powder like consistency but keep coming back in the same spots.

One thing I've noticed - the two actual black spot algae patches (where they don't brush away at all and even have a bit of a membrane around them) attract this same black stuff around them. Thats what makes me think somehow it has spread from those two spots and started forming in other areas... even though the other stuff just brushes away. See the pic below (pool is blue, iPhone has got the colours wrong - its not green!)

 

Tepelus

LifeTime Supporter
Jun 4, 2014
121
Oslo
Use an opaque cover. It will starve the algae of light and protect chlorine, so you have a win-win situation. If you do not have one, get one. It is a wise investment since the SWG will have to work less, therefore it will last longer. How is your circulation? Do you have the pump on 24/7? Local concentration of chlorine is normally depleted in the areas with algae. You need to make sure that water is well mixed up everywhere. Problematic areas are the steps, corners and surfaces in general. Ruff surfaces have to be brushed more often.
 

drewh

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

Hi Tepelus, thanks re cover I did consider it years ago but the build up of leaves etc. talked me out of the idea (every person I know who got one stopped using it).

The bigger issue for me is working out if this stuff IS algae - is black but brushes away easily. It will literally reappear within 1 to 2 days, and as said earlier I've tried bombing it with chlorine plus many other things to no avail.

When I get the TF-100 test it I'll SLAM it & that should rid it, but in the meantime I'm trying to eliminate other stuff. It definitely seems something unusual.

You're right the black spots will appear in the middle of the pool where the water movement is less, but now even right underneath the return jets, there's a patch.
 

Tepelus

LifeTime Supporter
Jun 4, 2014
121
Oslo
All organic debris will use up chlorine, not only algae. Water has to be as clean as possible. Better buildup of leaves on the cover than in you pool. You have to clean the filter as well. Lookup the deep wash procedure. Keeping everything clean you maximize your chances of success. Do you have a main drain? If yes make sure that all the intakes including the main drain are operational. Best water circulation is achieved if the flow is divided evenly between all the intakes. If you do not have a main drain, make sure that some return jets are pointing downwards. Make sure that you do not have a separation layer with hot water on top and cold water on bottom. If you have this situation, you may have sufficient chlorine on the surface layer, but not enough on the lower level. Take a water sample close to the bottom and test it for FC concentration. Make sure that you do it slowly without disturbing the separation layer yourself.
 

jblizzle

Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
43,238
Tucson, AZ
Re: Black (I think?) Algae that will not go away - any help appreciated!

To what pH buffer are you referring to? TA is a pH buffer. Borates can optionally provide additional pH buffering.
 

drewh

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

jblizzle, sorry that's what I meant - I've rarely had to increase TA as my pH usually creeps up so I'll add acid and lower them. But when I get the test kit (!!) I'll adjust both. You recommended a lower pH earlier in the thread, say 7.3, would you recommend I go for a higher slightly higher TA then to try and stop the pH rising as it does?
 

drewh

Well-known member
Oct 19, 2014
101
Brisbane, QLD, Australia
You have to clean the filter as well. Lookup the deep wash procedure.
Ok I'll look it up thanks. Yes I backwash the filter every 4 weeks or so, see earlier in thread.

No main drain only a skimmer & suction line.

Both return outlets do point slightly down vs straight out

Make sure that you do not have a separation layer with hot water on top and cold water on bottom.
How would I easily test this? The pool isn't particularly deep so I wouldn't *think* this is the case. Whenever I would take a sample to the pool shop I'd reach down about 50cm and take it from there. When I get the test kit will get into the pool & take a sample right at the surface of the plaster and test.
 

jblizzle

Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
43,238
Tucson, AZ
Re: Black (I think?) Algae that will not go away - any help appreciated!

jblizzle, sorry that's what I meant - I've rarely had to increase TA as my pH usually creeps up so I'll add acid and lower them. But when I get the test kit (!!) I'll adjust both. You recommended a lower pH earlier in the thread, say 7.3, would you recommend I go for a higher slightly higher TA then to try and stop the pH rising as it does?
The higher the TA, the faster the pH will rise. I am not going to recommend a pH value before seeing full test results.
 

chem geek

TFP Expert
LifeTime Supporter
Mar 28, 2007
12,083
San Rafael, CA USA
If it brushes away easily and poofs away dust-like, that isn't black algae. That sounds more like yellow-mustard algae except that it's not usually black and it usually doesn't like sun so would grow on the shadier side of the pool. So perhaps this is more like a green algae except darker or it's not algae at all.

You say the CYA level is only 40 ppm, but this is a pool store test and they are notoriously inaccurate. You might also have dirt or pollen getting into your pool and could use a skimmer sock (or panty hose over the skimmer) to see if you collect anything that looks similar to what is collecting on the bottom.
 

Tepelus

LifeTime Supporter
Jun 4, 2014
121
Oslo
If you have a significant temperature difference between surface and deep end when the filtration system is working, then you have may have a stratification problem. Cold water sits on the bottom of the pool while the warmer water is closer to the surface and gets circulated and chlorinated. If the two layers do not mix, than the deeper colder water does not get chlorinated. You can test this with a thermometer. Measure the water temperature close to surface and at the deep end. You can visualize the water circulation by injecting a drop of dye (beetroot juice for example) closer to the place where algae grow.
 

drewh

Well-known member
Oct 19, 2014
101
Brisbane, QLD, Australia
Really appreciate everyones help and advice, such a great community - thanks guys!!

Here's the link to deep cleaning a sand filter...
Thanks Butterfly I'll do that this weekend - when I opened the filter the sand/media looked an orangey colour, but obviously just different sand. I bet there will be heaps of crud that comes out!

If it brushes away easily and poofs away dust-like, that isn't black algae. That sounds more like yellow-mustard algae except that it's not usually black and it usually doesn't like sun so would grow on the shadier side of the pool. So perhaps this is more like a green algae except darker or it's not algae at all.

You say the CYA level is only 40 ppm, but this is a pool store test and they are notoriously inaccurate. You might also have dirt or pollen getting into your pool and could use a skimmer sock (or panty hose over the skimmer) to see if you collect anything that looks similar to what is collecting on the bottom.
This is what has puzzled me. There IS the two definite black algae spots (pics are in this thread) in the deep end and this other black stuff is around that, as well as all over the pool in other spots. But everything (exc the two black spots) brushes away quite cleanly before returning the next day or second day after, in the same spots (only those two spots don't budge no matter how hard I brush). Last season I would literally be down there every day brushing the whole pool, trying everything to stop it reforming, but as said earlier every thing I tried has failed (including the copper based algaecide, which if at all only marginally improved things - not much). I will be so happy once I rid the pool of whatever this is.

Also like the skimmer sock to see if anything gets trapped, re dirt, will do that. Re CYA, I actually measured myself the exact amount to bring the chemistry to 40ppm (knowing the precise volume of the pool), and the last time I tested it last season it was 8, so I assumed it would be close to 0. That would mean the test coming out at 40 would be fairly accurate. Looking forward to getting an exact reading using the test-kit when it arrives (it'll feel like Christmas - lol).

If you have a significant temperature difference between surface and deep end when the filtration system is working, then you have may have a stratification problem. Cold water sits on the bottom of the pool while the warmer water is closer to the surface and gets circulated and chlorinated. If the two layers do not mix, than the deeper colder water does not get chlorinated. You can test this with a thermometer. Measure the water temperature close to surface and at the deep end. You can visualize the water circulation by injecting a drop of dye (beetroot juice for example) closer to the place where algae grow.
Really interesting, I will measure the temp diff including the drop tests to check how the water circulates in spots - it might be exactly whats happening. What if I tried sitting a triclor puck on an area of the black algae patches, pushing it around for 30-45 mins. Then seeing if the algae reappears? I have actually been meaning to use a triclor puck on the two actual black algae spots (brushing 2-3 times daily and then sitting the puck on it for 30 mins, repeating etc.). Hopefully very little CYA will be added because I'll just sit the puck in there for a short time then take it out.
 

singingpond

Well-known member
Sep 15, 2013
728
Connecticut
...the problem is the only spots I can try this are the shallow and deep end steps. When I try to lift some of it, it just blows away like powder (literally that consistency)....
How are you trying to 'lift' the material? Can't you get close to it with an eyedropper, or something of that sort, and just suck up a small quantity without making it all dust up and disappear? You just need a small sample to try the test chem geek suggested.
 

drewh

Well-known member
Oct 19, 2014
101
Brisbane, QLD, Australia
How are you trying to 'lift' the material? Can't you get close to it with an eyedropper, or something of that sort, and just suck up a small quantity without making it all dust up and disappear? You just need a small sample to try the test chem geek suggested.
Thats a great idea re eyedropper. I had tried using a few things including the net, a scraper on it (the algae is on the pool floor and even midpoint of the pool, its not really easy to reach down and grab some. I was trying to think of another way to take a sample, the eyedropped for the very shallow end might work.
 

drewh

Well-known member
Oct 19, 2014
101
Brisbane, QLD, Australia
Update all.... got my TF-100 kit!! (feels like Christmas already). Was definitely worth all the effort to send to Aus, it's great and very easy to use. The CYA test was a bit tricky (how obscured should the dot be?) but I took all measurements.

My pool is blue and looking good except the algae still reappears and is there now quite a bit. See pic at end to get general idea.

These are my results using my shiny new TF-100 kit:

pH 7.5 (pen I have also showed 7.5)
FC 7.5
CC 0-1 (first time I wasn't sure if there was very slight pink and second time almost sure none, so it's either 0 or slightly above that)
CH 300
TA 120
CYA 30 (tested a few times but wasn't sure how obscured the dot should be - pool shop test last week was 35).

As said earlier, the black algae has been there for some time but always brushes completely away. The pool cleaner picks up some of it & the rest just gets darker till I brush it.

Should I tackle the two actual black spot algae marks (see pics at start of thread) first before SLAMing? My plan of attack was brush the marks vigorously with a stainless steel brush, then sit a trichlor puck on it for 45-60mins, take it out, repeat till its gone.

I'll do an OCLT tonight and see what it reads tomorrow (I don't need to retest the FC again tonight do I? Only did the test an hour ago).

 

drewh

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

Just took sample now, and result of OCLT is 0.5 ppm loss (FC 7.5 at midnight last night, 7.0 just now). Even with this algae growth..... what does that mean? I was expecting it to have used more chlorine.

On this basis I'd already pass the criteria to stop a SLAM and I haven't even started.

What are people's thoughts on this? Hoping it is just algae..!
 

jblizzle

Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
43,238
Tucson, AZ
Re: Black (I think?) Algae that will not go away - any help appreciated!

If you see algae, you have not passed the "clear water" requirement.
 

drewh

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

Also just one other quick follow up if I can. My CYA is about 30 using the TF-100 kit with some level of subjectivity.. a few times 26/27 and also 32/33. But about 30 with the dot being all but covered (still very slightly visible). Pool shop test was 35. Should I use the 40 CYA shock level of 16 to be on the safe side, or 12?