Black Algae Question

[Cayman]

If someone has black algae, does it affect the CC like regular algae does?

I noticed a few black spots on my steps yesterday and was curious because my CC is now at 0. The few spots are black, round and almost look like mold. On a couple of them, the other area of the circle is lighter in color than the center. Almost like it fades to a transparent on the outer area.

I took a few pictures that I will post tonight but figured I would go ahead and ask a few questions to get things started.

Thanks!!

 

[Guest]

If someone has black algae, does it affect the CC like regular algae does?
Not Always!

Black algae happens after and extended period of pool neglect, either too low a FC level for an extended period of time or way too high a CYA level. It would be helpful if you post a full set of test results.
An easy experiment you can do is brush one of the spots with a wire algae brush and then hold a trichlor tablet on it for about an hour. If the spot is black algae it will be gone so greatly reduced.
The only cure for black algae is a LOT of brushing with a stainless steel algae brush and VERY high FC levels for a period of time, usually about a week or so.

 

[Cayman]

waterbear... I have started posting my most recent test results in my signature. I thought this would be a good idea as it is so often needed in certain situations. :-D

I would say that there are about 6 small spots on my steps. That is the only place I see them. I will be sure to try your suggestion and post the outcome.

Also, keep in mind that I had an algae breakout a couple of weeks ago and my FC has been between 20-40 since then.

 

[Guest]

waterbear... I have started posting my most recent test results in my signature. I thought this would be a good idea as it is so often needed in certain situations. :-D
The problem is that the signature is NOT visible when you are posting a reply so I was not able to see the test results. It would be helpful if you could include them in the body of the post so they can be referred to when someone is answering a post.

I would say that there are about 6 small spots on my steps. That is the only place I see them. I will be sure to try your suggestion and post the outcome.

Also, keep in mind that I had an algae breakout a couple of weeks ago and my FC has been between 20-40 since then.

With a CYA of 70 ppm you would need to maintain FC levels of 35-40 ppm MINIMUM for black algae, maybe up to about 50 ppm, and ALSO be brushing with a wire algae brush several times a day (a combo brush is not going to cut it here!).
The point is your water has had problems so it is entirely possible that black algae has taken hold. It's growth might be slowed by the high FC but it is possible for it to grow under those conditions, especially if the spots are not being brushed several times a day.
Try the trick with the trichlor tab and the algae brush. If it makes the spot lighter in color or smaller then it's a good indication that you have black spot algae. If you only have a few spots I would treat them with granular trichlor (from the poolstore, it's not easy to find but I know where you can get it in St. Augustine ). It's the easy way to dispense high chlorine doses directly on the spots and it won't have that great an impact on your CYA since you only have a few spots to treat. Brush the spots well before applying the granular trichlor. You can do the same thing with a trichlor tablet in a white cotton sock held on the spot with your pole but you can only treat one spot at a time that way and that can be a headache.

 

[Cayman]

OK.... I picked up a Trichlor Tab and brushed one of the spots and now I am letting it sit there on the spot. Luckily these spots are on the step which is only about 6" deep.

After brushing the 2 spots in these pictures pretty good with an all steel brush, they did not change or fade or anything. Here are a couple of pictures. Not sure if they will help or not but figured it was worth a try.

 

[Cayman]

The spot in the 1st picture is now gone after an brushing with the steel brush and then setting the trichlor tab on it. All that is left is a very very faint yellow/gold mark.

So is this black algae I guess? :?

 

[chem geek]

Most likely it is black algae. A Trichlor tab will lighten most organic stains. It will not usually lighten a metal stain (ascorbic acid usually will do that, especially for an iron stain).

 

[Cayman]

The trichlor tab removed the 1st picture but did nothing for the spot in the second picture. I only see a few others so I guess I will spot treat them and see where that puts me. If there are others on the bottom, I can not see them. I only see these on the top step.