Green pool not consuming chlorine during SLAM

rwm

Member
Jul 7, 2019
6
MA, USA
Hi, all. I opened my pool (18k gallons, plaster) this past Saturday to find a very murky green, unlike I've ever seen it before. I decided to try to treat it rather than drain. I adjusted pH to ~7.2 and added stabilizer to get to 25-35 CYA.

When I mentioned the algae to the pool store owner, she recommended starting with some non-chlorine shock so I added 2 lbs of 45% Potassium Monopersulfate on Saturday afternoon. Apart from that, I have been following normal SLAM. It's been about 3 full days now and I have not seen much if any improvement in the water, in color or clarity. The pump has been running 24/7 and pressure is normal. I opened it and cleaned the cartridges once after a couple days, just to make sure that it was filtering properly, and got plenty of algae off, but it was by no means saturated.

The weird thing, though, is that almost no chlorine at all is being consumed. Last night, overnight, it somehow gained 1 part (I assume testing error). These are the most recent readings I recorded, starting yesterday at 12:30p, using a new FAS-DPD test from the TF-100 kit:

Time / FC / Addition oz 12.5%
12:30 / 13.5 / 0
14:15 / 13.5 / 0
16:32 / 13.5 / 0
18:30 / 11 / 41
22:00 / 17 / 0
09:30 / 18 / 0


I didn't write down the previous measurements, but it was sticking right around 13.5 back into the previous day as well. So I have no idea what's going on here. There is no chlorine feeder or any source of chlorine other than the bleach I'm adding. Why is virtually no chlorine being consumed when the pool is still solid green? Why did adding 41oz bleach raise the FC that much (pool calculator said it should raise it by 2.2)? Is that initial non-chlorine shock throwing things off even after 3 days? I would just keep up the SLAM but I'm burning through my FAS-DPD kit just to find no change over and over again. I'd be very grateful for any input.

For an idea of how green we're talking, the step that can be seen in the lower left of the picture is about 20 inches below the surface. (Sorry for the reflections, it's really hard to get a decent picture of this.)IMG_20200502_190317.jpg
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
17,969
Northern NJ
We recommend you do not mix advice from different sources. Mixing pool store and TFP advice can confuse things and send you down wrong paths.

I wonder if we are looking at water that has a copper problem and not an algae problem.

@mknauss @JoyfulNoise you have ideas about what is going on here? Is the MPS giving false chlorine tests?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
29,270
Laughlin, NV
I do know that MPS produces incorrect FC/CC test results. There are reagents to counteract that, K-2041 (0.75 oz) or K-2042 (2 oz).

How long it will last I do not know. I do not think the MPS is oxidized like chlorine. But Matt can help us out with that.

If the pool is cloudy, you have organics in the water. You have to SLAM those away and then deal with metals.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
16,905
Tucson, AZ
2lbs of MPS in 18k gallons isn’t a lot but it will mess up the FAS/FPD test for a good 48hrs or more if the water is cold. MPS doesn’t turn DPD pink but it will consume drops of R-0871 making the FC appear falsely high. It can also make CCs appear high as well.

At this point all you can do is keep adding chlorine as needed to stay at shock level, brush, vacuum and clean the filter. Honestly that water looks a very deep green to me which is darker than what I would expect from metals.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
17,969
Northern NJ
added stabilizer to get to 25-35 CYA
Confirm if your CYA is 30 or 40. There is no 25-35. If the dot disappears between 30 and 20 we round up and call it 30.

If the dot disappears between 40 and 30 we round up and call it 40.

SLAM FC for 30 is 12 and 40 is 16.
 

rwm

Member
Jul 7, 2019
6
MA, USA
Thanks for the advice everyone. The green has cleared up just by keeping up the shock level for another couple days, and now the water is a pleasant turquoise but still very cloudy after running the pump 24/7 for 9 days. I have vacuumed several times and brushed regularly, but it's a little tough because I can't see what I'm vacuuming. What's getting sucked up mainly looks to be fresh leaves & petals, not a ton of anything though.

I had gotten different CYA readings and also added stabilizer in the beginning, which is why I had it between 25 and 35. I just retested CYA at room temperature and it's right at 30. I'll adjust my FC target down to 12.

So, just stick with it? I assume I should not use any clarifier products?

2020-05-11.jpg
 

rwm

Member
Jul 7, 2019
6
MA, USA
@Ezun, thanks for the continued interest! It's making slow progress but definitely improving. I can see the bottom of the shallow end now. Had to get more R-0871 but now I have enough to keep this up all summer if I have to. Chlorine is definitely being consumed now.

IMG_20200516_100141.jpg

(That plaster on the steps is a whole other issue...) A new development this morning: we had a big thunderstorm last night that caused a lot of debris in the pool and the pressure gauge showed zero, so I cleared out all the baskets which were very blocked (including the one at the pump), and when I turned the pump back on, the pressure gauge still shows zero. There are new filter cartridges in there so it never gets that high anyway, but usually about 4. The actual flow at the skimmers and back out the returns is definitely not zero, although it does feel maybe a a bit weaker than normal. So I'm guessing the gauge just died overnight? It's only a couple years old. There's been a small leak at a fitting near the pump for a while that doesn't seem to have gotten any worse or anything. There is some new air in the system whenever I open the bleeder valve, though. Any thoughts on that or should the first step be to try a new gauge?
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
29,270
Laughlin, NV
If you pulled in a lot of debris at the pump basket, check the impeller. Turn off the pump at the breaker, isolate it, take the basket out and feel the impeller to be sure it is clear.