Black Algae or Mineral Stains?

[Nick79]

I have these little spots on all the sloping floor areas of my pool. They aren't on any vertical walls, they aren't on the stairs. The way it streaks gives me slight hope (denial?) that its just staining of some sort, buI really have no idea. The streaks are all oriented toward the main drains. Black algae or staining? Best guesses?

 

[Texas Splash]

Has it been windy in your area? It almost looks like something blew into your pool and slid down the walls causing those trails. The pic gives almost a greenish impression of the water. Is that just an illusion of the picture, or is there some green in the water as well?

Also, please tell us how you are chlorinating at the moment (bleach I hope) , and what test kit you are using. Can you post a full set of results? It might help.

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Do those things change at all with brushing?

 

[HiddenRiver]

The green water tells me there is an imminent problem...and the little black dots may not be the major one, although it doesn’t look that different than how my black algae problem started-streaks on the bottom of the pool

 

[Nick79]

The water is a bit green, but not as green as that picture makes it look. I've been keeping the chlorine at 5ppm for the last few days, but I think the color is due to the high pollen levels right now in east TX. The black spots do not go away with brushing. Neither a plastic or wire brush has any effect on them.

I'm using 10% HDX bleach from Home Depot. I have a Taylor K-2005 test kit and the numbers from yesterday are:

FC - 5ppm
PH - 7.8
TA - 160
CYA - 110
CH - 180

Overnight Chlorine Tests have been showing 0-.5ppm drop.

 

[Texas Splash]

You have a couple issues at the moment to contend with - stains and algae. There's a chance they could be related, but I've never seen a stain have that "run" effect like a shooting star. That still looks like something was blown into the water (like fertilizer or weed & feed perhaps). Let's start with the algae though. Your CYA is crazy high. Since there's no way our CYA viewing tubes give an accurate number of 100, you might try the dilution CYA test as seen HERE, starting at Step #8. The CYA for your pool (no SWG) should be no higher than 50 right now. Because your CYA is so high, the FC can't keep up. Once you have an accurate CYA number from the dilution test, then you'll know how much water to exchange to lower the CYA.

Speaking of FC testing, the K-2005 only goes so high. By adding the FAS-DPD testing portion to your current set-up, you essentially make it a K-2006 kit. That's what you need. That has to be a priority so that you can perform a TFP "SLAM" link below to kill & remove the algae. Remember to follow everything on the SLAM page correctly for best success, to include lowering the pH to 7.2 before starting the SLAM.

Going back to the stains, you can try placing a chlorine tablet on an area to see if it changes. If not, then try some Vitamin C tablets crushed-up and in a sock and let that sit for a little while. I'd start with those two first and see what reaction you get.

 

[Nick79]

Thanks for the replies. I did the dilution to measure the CYA. I know it's high, I just bought this place and there were chlorine tabs in the inline feeder when i moved in. I'll get the additional test kit items. I've got enough bleach to start a SLAM tonight. I'll see what results I get from the vitamin C and tablets and go from there. Thanks again.

 

[Nick79]

2 points to update.

A chlorine puck dissolves the stain as if it never existed. What does that tell you about the stain's origin?

I got the fas/dpd reagents.

FC - 5ppm
Cc - .4ppm

I think that's good, right?

 

[Texas Splash]

A chlorine puck dissolves the stain as if it never existed.

Organic staining - i.e. algae. So that means chlorine (the proper amount for your CYA) is required to SLAM and clear it all from the water. Now your CC of .4 is good in that it is just under .5 which is our limit for concerns. Your FC of 5 may sound good on the surface, but I suspect it is way too low. Why? Take a look at the Chlorine/CYA Chart (link below). If someone's CYA is 100, their minimum FC should be 8 before algae starts to be a concern. If your CYA is over 100, then it becomes increasingly difficult to match the FC and CYA. Since your K-2005 has an FC testing limit, you are really stuck. So the sooner you get the FAS-DPD to test FC at much higher levels (to perform the SLAM) the better. Were you able to do the diluted CYA test? After getting that number and multiplying by 2, what CYA did you get? That will tell you how much water you need to replace to lower the CYA.

 

[Nick79]

The originally reported cya of 110 was done through the dilution method some the 2005 test kit only gives values up to 100. I diluted, got 55ish and multiplied by 2 to get 110.

I have the fas/dpd test kit now. More specifically, I bought r-0870 powder and r-0871 reagent to add to my current kit. I used those to get the FC 5ppm and cc
.4ppm results.

I'm going to slam tonight even with the higher cya levels. I know it'll require more chlorine, but I don't want to wait to drain/refill. The cya has been trending down over the last month or so from 140+ to now 110. More rain in the forecast should only help that I guess.

 

[Texas Splash]

I diluted, got 55ish and multiplied by 2 to get 110.

Perfect!

I have the fas/dpd test kit now. More specifically, I bought r-0870 powder and r-0871 reagent to add to my current kit.

Even better!

Certainly your choice to not do a water exchange. Your SLAM FC level will be high, around 43-44 or so. That's a lot of R-0871 drops. For now, you might consider using the 5ml water sample so that each drop equals 1ppm. No multiplying or dividing that should save you a bit of reagent. It's not quite as accurate (unless you have a syringe), but at this point it might help. Good luck!

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Remember - Use only regular bleach for the SLAM. I would recommend HEB's regular Bravo (8.25% at $2.94 per gallon) since I heard Walmart's Great Value strength was lowered. But you can shop around for the best deal in your area.