So I used some copper algaecide to try to treat black algae. Didn't work. Now what?

JCD3nton

Member
Jul 6, 2020
15
laredo
I have the big Taylor test kit that comes recommended (it was ~$60 or so).

No other potions or snake oil.

The pool is losing chlorine whether daytime or nighttime. It just doesn't hold it at all. Pool is out of direct sunlight so I just put in enough to raise chlorine ~20ppm, I guess we'll see what happens now. It definitely seems like this stuff is having a harder time dissolving than normal. Like I can see particles, hanging, suspended in the water.
 

Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
4,565
NW Ohio
I really, really don't think algae is doing this.
I don't see any reason to say that. Algae is invisible until it's grown so much that it become visible, but it can be a significant problem LONG before then.

Everything you are describing sounds very much like an algae (or other organic) issue. On what basis do you believe that can be ruled out?
 

JCD3nton

Member
Jul 6, 2020
15
laredo
Well I'm at a loss here. The pool finally held some chlorine, but I stayed up late last night gaming and tested it several times throughout the night and it's definitely losing substantial amounts (10+) even at night.

It's way too much lost to be algae. I think I've put in 40+ ppm in the last 24 hours. That's a lot more than it has taken in the past to clear the pool when it was completely neglected and turned opaque dark green. I don't see how that amount of algae could be present when the water is clear, and the pool chlorine levels had been stable for a week before, then shocked.

Anyways, last I tested, I had about 10 FC in the water. I finally remembered to test for CC, and that is at . . . 7. Not sure if something is interfering with the test or it's really that high.
 

JCD3nton

Member
Jul 6, 2020
15
laredo
For those curious, or anyone who ends up in the same situation and is looking at this for reference, it appears that the blue substance in the algaecide (whatever it is) is what was causing the chlorine loss.

Water had a major blueish tint ever since adding the algaecide (in fact, when I poured it in, it looked like blue food coloring). After adding all of that chlorine last night, the pool is now finally holding chlorine, and simultaneously, the blue tint completely disappeared.

Luckily I do not have green water or oxidized copper all over the place, which was my fear.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,216
Tucson, AZ
The blue color is from the copper sulfate. It’s not a dye. It’s the color of an aqueous solution when copper sulfate is dissolved.

If your CCs are as high as that last post, then you have a problem. 7ppm CCs is off the charts high and your water would stink of chlorine if it were that high.

I’m suspecting testing error. If the FC is too high it will bleach out the DPD indicator and cause a false low reading.

How many scoops of powder are you adding and what size water sample are you using?
 

JCD3nton

Member
Jul 6, 2020
15
laredo
Pretty sure I'm doing the test correctly. Just ran another one.

(1) Two scoops of powder added to 10ml sample. Water turns dark pink.
(2) 13 drops of the second reagent turn it clear. At .5ppm per drop i get 6.5 FC
(3) Instructions say to add 5 drops of the third reagent to test for CC. Water turns dark pink again
(4) It took 10-12 (may have miscounted by 1) drops of second reagent to turn the water clear again. So let's say combined chlorine is ~5.5

I checked and the water may have a light chlorine smell. Does not "stink" of chlorine though. I have smelled that strong chlorine smell after clearing severe algae blooms and it's nothing approaching that. I backwashed my filter to check, which is the scenario where I have smelled strong chlorine before.

Good news is the chlorine hemorrhaging has stopped.

Not sure what my next move is here. Also, can I test for CC without testing for FC first? Running low on the second reagent and I have a cheapie kit from walmart that can at least confirm that FC is in the 5-10 range.
 

mguzzy

Gold Supporter
Jul 8, 2015
2,205
OV, CA
Not sure what my next move is here. Also, can I test for CC without testing for FC first? Running low on the second reagent and I have a cheapie kit from walmart that can at least confirm that FC is in the 5-10 range.
You have to measure the FC first to get to CC with this particular test. If the aqueous copper was not[edit] reacting with your chlorine then there was something else going on. Some other combination of chemical reactions. You should not be smelling chlorine at all when the pool is balanced. I would still be concerned about where the copper went. @JoyfulNoise do you think it should be sequestered?

PS: can you fill in your signature so we have an easy reference for the kind of pool equipment you have? thx
 
Last edited:

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,216
Tucson, AZ
Copper and chlorine don’t react, period.

There is something else going on here. The CC levels, if accurate, suggest that there is something else in the water combining with the chlorine. There are copper scale removal chemicals that will cause false-high CC levels and non-chlorine shock (MPS) can cause false readings as well.

The only two avenues of inquiry here are a complete list of every chemical added to this pool AND check you test kit for expired or bad reagents. If the FAS titrating drops (R-0871) are bad, that will cause a false-high reading.
 

JCD3nton

Member
Jul 6, 2020
15
laredo
Nothing else has been added to the pool: chlorine source, CYA, muriatic acid. That's all I've ever used, except a clarifier a couple of years ago. The algaecide was a new, last resort thing to see if it would help the rest of the black algae come off.

Joyful, you may be right about the reagents. The R0871 "expired" two years ago although it does not show yellowing as taylor says indicates a compromised reagent. It's still clear. Sort of moot since it's running low anyways: Recognizing A Compromised Reagent

The powder doesn't look so hot though. It's purpleish.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
17,216
Tucson, AZ
Nothing else has been added to the pool: chlorine source, CYA, muriatic acid. That's all I've ever used, except a clarifier a couple of years ago. The algaecide was a new, last resort thing to see if it would help the rest of the black algae come off.

Joyful, you may be right about the reagents. The R0871 "expired" two years ago although it does not show yellowing as taylor says indicates a compromised reagent. It's still clear. Sort of moot since it's running low anyways: Recognizing A Compromised Reagent

The powder doesn't look so hot though. It's purpleish.
Your reagents are compromised. You need new ones. Your FC/CC results are not trustworthy. The FAS drops don’t have to turn yellow to be compromised.

Use a simple OTO (yellow total chlorine test) until you can get new reagents.
 

JCD3nton

Member
Jul 6, 2020
15
laredo
Should I just replace the chlorine regeants from my K2006 or do the others also have short shelf lives? Most of the others haven't really been used much, other than CYA, and I just bought a big bottle of that.
 

JCD3nton

Member
Jul 6, 2020
15
laredo
I grabbed the test kit refill. Hopefully they ship it pretty quickly.

Whatever caused this from the algaecide seems gone. It's holding chlorine normally again, all of the dark blue tint to the water is gone. The CC is down below 1 (it's been progressively decreasing yesterday and today). Actually seems like some black algae went away too, although I'll have to get up close underwater to have a better look at it. Maybe the algaecide did help some, because previously, high levels of chlorine did nothing to it.

The only odd thing I noticed is that the cal hypo turned dark grey today when I dumped it in. I was surprised by this . . . I turned around and saw a dark pile of the stuff about a minute after I put it in. I quickly brushed it away but it left a dark stain on the pool (which is fortunately now gone). Maybe it oxidized some copper?

Now that the pool is behaving "more" normally, I guess I need to figure out if I have a "copper problem" or not. Only people who will use the pool in the foreseeable future are me and my girlfriend. I was thinking of "borrowing" a small amount of her blonde hair and seeing if it turns green or not in a bucket of pool water. :geek: