SLAM normal length of process?

PoolBrews

Well-known member
Oct 16, 2019
186
The Villages, Florida
Hello!

My water was looking a little cloudy, so I decided to SLAM it. I'm fairly new to the SLAM process.

Notes:
I'm running my SWG during the day to maintain the chlorine levels.
I have a solar cover that I put on in the evening (around 7pm) and take off in the morning (around 10am).


Below are my results so far:
Day 1:
CYA is 60​
Raised FC to 24 in afternoon.​
Checked at 7pm, FC was 19, added liquid chlorine to bring it back to 24.​
Recorded FC at 8pm: 27​
Turned off SWG​

Day 2:
Checked FC before sunrise: 19.5​
Overnight chlorine loss: 7.5​
Water crystal clear.​
Brought FC back up to 24 using liquid chlorine​
Turned on SWG​
Checked at noon - FC was 21 - added 10% liquid chlorine using pool math.​
Upped my SWG to maintain - (May have upped it too much :))​
Checked FC at 9pm: 30​
Turned off SWG (and dropped % significantly - from 50 to 25)​

Day 3:
Checked FC at 7am: 24​
Overnight chlorine loss: 6.0​
Water crystal clear.​
Turned SWG on.​

Questions:
  1. It looks like I'm still losing around 6ppm of chlorine overnight - is this normal?
  2. I'm assuming that if FC is at 24 after sunset, it should be 24 before sunrise?
  3. Should I expect my overnight loss to drop each day?
  4. Is this number of days to SLAM a pool normal?
  5. Any chance there could be something on the solar cover that could be contributing to this?
Thanks in advance!
 

PoolBrews

Well-known member
Oct 16, 2019
186
The Villages, Florida
I'll turn it off, but would like to understand the reasoning behind leaving the SWG off during the day. I don't see why this would in any way affect my overnight readings as long as the SWG is off between the times that I take my evening and morning readings.

My thoughts were that instead of checking chlorine levels every couple of hours, I could raise it to the min FC needed, then let my SWG resupply the small amount of chlorine that is lost during the process during the day, and only check 3 times a day. Kind of like a buffer during the day when loss is expected. Overall, it should keep my chlorine levels elevated where they need to be.

Or is there a specific scientific reason as to why I shouldn't do that?

Thanks!
 

borjis

LifeTime Supporter
Aug 19, 2014
3,096
Pacific NW
Slams seem to be 1 to 3 weeks depending on the foothold the algae has taken. I don't have an swg, but don't see the harm in using it if you turn it off so it doesn't throw the overnight test. But that could be wrong I suppose.
 

Flying Tivo

Well-known member
Jan 24, 2017
1,411
Monterrey, NL, Mexico
The SWG generates very slowly, and putting the SWG through the strain of outputing 24hrs a day is not cost effective. The plates degrade with use and for slam you should use liquid chlorine since its cheaper.
 

Newdude

Well-known member
Jun 16, 2019
2,433
NY
The SWG generates very slowly, and putting the SWG through the strain of outputing 24hrs a day is not cost effective. The plates degrade with use and for slam you should use liquid chlorine since its cheaper.
I did the breakdown for mine per the 10k expected lifespan hours. It costs 7.77 cents an hour to run. Or $13.05 per week of 24/7 output. If you hired a pool company to install one for $1500, it costs 15 cents an hour or $25.20 a week of 24/7.
 

PoolBrews

Well-known member
Oct 16, 2019
186
The Villages, Florida
I wasn't running it at 100% 24x7 - I was running it at my normal setting of 15% 24x7. I only bumped it up to 50% for a 4 hour period during my 1st day.

I'm not putting any more strain on it than I normally would. So, the only real reason to turn off the SWG during a SLAM is to save wear and tear on the cell, and electricity costs, correct? My concern is getting enough liquid chlorine to maintain due to shortages at my local store.

Back to my original primary question - does SLAM normally take days, or weeks?
 

goody222

Silver Supporter
Feb 6, 2018
127
Chesapeake, VA
I also have used my SWG during a SLAM during the day (not at night of course). So I will raise my FC to just above the calculated SLAM level and set the SWG to 50% (its normally 30-50%, so I don't see how this is reducing the life of my cell). It helps keep the FC at SLAM level. I've done 4 or 5 SLAMS before and I'd say mine last 6-10 days, depending on the severity. Just remember to brush every day and get all the nooks and crannys (the lip under my steps and the underside of the ladder steps are always trouble spots for me).
 

tim5055

Mod Squad
TFP Expert
LifeTime Supporter
May 11, 2014
10,728
Franklin, NC
Back to my original primary question - does SLAM normally take days, or weeks?
Normally, weeks. Bad pools can be over a month.

From what you are showing, you are doing the absolute minimum we recommend, testing and adjusting the FC to SLAM level 3 times a day. The SLAM's that go quicker are generally the ones where folks test and adjust back to SLAM level multiple times a day, say 6 or seven. I'm not adverse to seeing it done every 90 minutes with the pump running.

As to running your SWCG-

A brand new T-15 will produce 1.45 lbs of chlorine gas when running 100% for 24 hours. This would raise your FC by6.9. Running it even at 50% for 12 hours a day is only adding 1.75ppm FC which is basically an insignificant amount during a SLAM.Turn it on, leave it off, it's your decision. A cell has a finite amount of chlorine production in it. When it dies, it dies. We say turn it off because we expect you to be adding liquid multiple times a day anyway, so why use up part of it's life?

So, increase the number of times you test and adjust back to SLAM per day and it will go faster.