SLAM taking a lot of time and chlorine

Tobim

Member
Jun 7, 2019
8
Miami
Hi, all!

I have done SLAMs before, but this one seems to be slower than usual.

I was gone for a bit and pool-care arrangements did not work out so well (let's say), so coming back there was a fair amount of algae growth on the walls, but water was still clear. I measured the chlorine with the powder+drip test kit and got to VERY little (like 1 ppm; the test water barely changed color with the powder).

So I tested CYA (at 45) and pH and then went to SLAMming, using 10% "chlorinating liquid" (sodium hypochlorite, from Home Depot). I am only adding chlorine twice per day, but each time I am down to 7-10 ppm (from 20 which is my recommended SLAM level) within a half day. This has been going for 5 days now, although the last two days I was down to only 12-13 after a half day. Water looks nice, and walls a clearing up nicely (doing hand brushing, running my robot 5-6 times a day, and washing cartridge filter regularly, like every day or lately every other day). I never really had any big amounts of combined chlorine (max 1ppm).

For a 12000 gal pool, I have used about 10 gal of 10% bleach thus far.

Am I doing something wrong? I have done 1-2 slams on the same pool in the past, and they haven't taken this long or this much chlorine.

Thanks!

P.S.: I am in South Florida and it's been nothing but sunny, so I'm sure daytime sunlight burnoff is fairly high. But the overnight draw-down has been substantial, too and is only decreasing slowly.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
26,711
Laughlin, NV
Welcome to the forum!
The time a SLAM Process takes depends on organic load, number of times each day you test and raise your FC to SLAM level, and how often you brush the pool. Most SLAM processes take 1 week or more.
Read the SLAM article linked above for more information.

Please fill out your signature. The information really helps us help you.

I suggest you read ABC's of Pool Water Chemistry.
 

Tobim

Member
Jun 7, 2019
8
Miami
Thank you, @mknauss, for your kind message. I am familiar with both sources that you link and I added a signature.

So the timing seems OK, then. Does it also correspond to other people's experience that the pool is still "eating" so much chlorine after five days? I'm still having to put in about 1.5 gallons of 10% bleach per day to get back to SLAM level.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
26,711
Laughlin, NV
FC is consumed by two things, organics and UV.
So if your CYA is correct, the FC should be shielded somewhat by the CYA. And overnight loss is fully organics.

Have you checked light niches, skimmers, etc that harbor algae. Also raising back your FC 3 or 4 times per day will shorten the time. Once you are only losing a small percentage of the FC between tests, then you can go to twice a day.