Preparing to SLAM

thephatp

Well-known member
Jul 8, 2018
46
Austin, TX
Moved from here.

I'd like to piggyback here, as I'm about to start a SLAM myself.

I'm trying to get rid of 2 tiny spots of black algae (both less than dime size), one small spot of green algae (less than a quarter), and the remnants of mustard algae (this was kind of bad, and I shocked it before reading here). That's been about a week. The black algae is still present, the green algae appeared after the shock (but in the spa, and I'm still working on getting my equipment working correctly). The yellow algae seems much better, but I'm not convinced I actually killed it--I don't think I got close to the PPM I needed to kill it.

Numbers from yesterday afternoon:
  • FC: 1.5
  • CC: 0.2
  • pH: 7.8
  • TA: 100
  • CH: 190
  • CYA: 50
I'm using the Pool Calculator to figure out what I need to target, and I have a few questions:
  1. For FC, when entering the % bleach, is that the % sodium hypochlorite listed on the bottle, or the % yield of chlorine (which is less)?
  2. Target FC for Mustard Algae under "Suggested Levels" says 24. The Chlorine-CYA chart suggests 20. I've read online and heard from a pool company that I should target 30. How is the calculator adjusting for targeted FC, and what level should I actually use?
Other questions:
  1. I want to lower my pH to 7.2 before treating. I'm going to pour acid in tonight to do that. Should I wait until tomorrow to start the SLAM?
  2. Do I need to worry about adjusting the CH before starting?
Hoping some of these questions may be relevant to others, which is why I posted here. If I should start my own thread, I can do that.
 
Last edited by a moderator:

jblizzle

Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
42,968
Tucson, AZ
1. The % for the bleach should be 6 or 8.25 or 10 or 12.5 depending on what you have
2. Depends if you are going to follow our SLAM process or the advice of some other pool guy. The SLAM process was designed to not put your pool and equipment at risk like very high FC levels can. Use 20ppm for the SLAM and then the 24 hour soak at 24ppm.

3. You can retest the pH after about 30 minutes and then add chlorine
4. No

Also not sure how you got 1.5 for FC and 0.2 for CC ... if you used 10ml of water (as you should), each drop is 0.5ppm
 

thephatp

Well-known member
Jul 8, 2018
46
Austin, TX
1. The % for the bleach should be 6 or 8.25 or 10 or 12.5 depending on what you have
2. Depends if you are going to follow our SLAM process or the advice of some other pool guy. The SLAM process was designed to not put your pool and equipment at risk like very high FC levels can. Use 20ppm for the SLAM and then the 24 hour soak at 24ppm.

3. You can retest the pH after about 30 minutes and then add chlorine
4. No
Thanks for the advice.

What is "the 24 hour soak?"

Also not sure how you got 1.5 for FC and 0.2 for CC ... if you used 10ml of water (as you should), each drop is 0.5ppm
I couldn't quite tell whether it was 1.4 or 1.6, so I averaged to 1.5. I was using the 0.2ppm test for 25ml test. Why should I used the 10ml test instead? Sorry if this is a dumb question. I'm very new to pool ownership, so still a lot to learn.
 

jblizzle

Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
42,968
Tucson, AZ
I assumed you read the Pool School article about mustard algae ... if not, do so.

Use 10ml so each drop is 0.5ppm, it is precise enough and saves a lot of reagent (especially when at SLAM levels).
 

thephatp

Well-known member
Jul 8, 2018
46
Austin, TX
Gotcha. I will definitely do 10ml for the SLAM. I was just hoping to get a more accurate idea of the current ppm, since I expected it to be a little lower.

I did read the article, but I'd already forgotten some of the details. I've tried to do a lot of reading, since this is the first time I've dealt with algae.

I am thinking I'll wait until the weekend to SLAM, because I won't be able to add bleach throughout the day to keep the levels high. I read somewhere to add bleach no more than every hour, and no less than twice a day.

Realistically, I could only add it once in the morning, a couple times in the afternoon/evening, and before bed. Is this enough to go ahead and start the SLAM now? Or should I wait until the weekend when I can do it all throughout the day?
 

jblizzle

Mod Squad
TFP Expert
LifeTime Supporter
May 19, 2010
42,968
Tucson, AZ
It is pretty common to start with exactly what you said, morning, home from work, before bed. Any extra is a bonus.

The best time to plant a tree is 10 years ago, the 2nd best time is now ;)
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
20,260
Laughlin, NV
Realistically, I could only add it once in the morning, a couple times in the afternoon/evening, and before bed. Is this enough to go ahead and start the SLAM now? Or should I wait until the weekend when I can do it all throughout the day?
That is most acceptable. You may find slow going at the start, but the sooner you start the SLAM, the better.
 

thephatp

Well-known member
Jul 8, 2018
46
Austin, TX
Appreciate the advice, folks. I've got a stainless steel wire brush coming today to rough up the black algae spots before I start it, then I'll get going tonight. Thanks!
 

proavia

LifeTime Supporter
TFP Guide
Feb 6, 2015
1,466
Chandler AZ
A couple points of clarification....

You reported a CYA of 50 and an FC of 1.5 in your results from yesterday - and the FC/CYA Chart advises a MINIMUM FC level of 4, with a target of 6-8. Allowing FC to fall below the MINIMUM of 4 is allowing algae to multiply. Don't allow FC to fall below the minimum for your CYA, based on the FC/CYA Chart.

SLAM level for CYA of 50 is 20. This is the FC level you should aim for when you add chlorine during the SLAM Process.

Once you have passed all 3 criteria listed in the SLAM Process instructions, you then raise the FC level to mustard algae levels for 24 hours - based on this article: Chlorine/CYA Chart (for simplicity, you can round up the decimal numbers). For your CYA of 50, that would be 29-30. Again, you do this ONLY AFTER you have successfully passed the SLAM Process.

During a SLAM Process, dose 2+ times a day. If you can dose more than 2 times daily, the SLAM should go a bit faster - especially during the first several days.
 

thephatp

Well-known member
Jul 8, 2018
46
Austin, TX
Thanks @proavia, @mknauss & @jblizzle.

I got the wire brush in today instead of yesterday, so I brushed out the spots of black and green algae. I retested and got the following numbers:
  • FC: 2.5
  • CC: 0.5
  • pH: 7.6
  • TA: 100
  • CH: 210
  • CYA: 50
  • Temp: 87°F
I've added some muriatic acid to try to get it down closer to 7.2. Then, I'll add the bleach according to the pool calc (505 oz).

Also, regarding the CH, how "blue" does the water need to get before you consider the test done? I've had a hard time with this one. It starts to turn purple around 17 drops, but doesn't actually turn blue until about 21. Then, not sure how blue it should be.
 

thephatp

Well-known member
Jul 8, 2018
46
Austin, TX
500+ oz only got me to 16.5 (an hour after putting it in), so I added another 100+ oz to get me to 20. I'll check again in the morning before the sun hits it and adjust as necessary.

I want to say I love the information available on Trouble Free Pools, and I greatly appreciate the help you've all given!

Added a subscription for the Pool Math app, too, to keep records of my tests. Love the simplicity of the app.
 

thephatp

Well-known member
Jul 8, 2018
46
Austin, TX
OK, just tested this morning and got 16ppm. I'm sure it's hard to say what "normal" is, since each algae problem is different, but you can't see any visible algae in the pool. Other than the 4 spots I scraped yesterday (which you can't see unless you're under the water with goggles on), maybe the mustard algae is really hard to see? Or is losing 4ppm overnight normal at the start of this process?

Should have asked this ahead of time, to set my expectations. ;)
 

Katodude

Silver Supporter
Aug 22, 2017
213
West Palm Beach/Florida
Losing 4ppm overnight is part of the process. You have algae. I remember last year when I had to do a SLAM I had one little spot of Algae and it dropped 6ppm overnight. Most of the algae is invisible. There is a bunch in there, you just cant see it. By the time you see some its an infestation.
 

thephatp

Well-known member
Jul 8, 2018
46
Austin, TX
Losing 4ppm overnight is part of the process. You have algae. I remember last year when I had to do a SLAM I had one little spot of Algae and it dropped 6ppm overnight. Most of the algae is invisible. There is a bunch in there, you just cant see it. By the time you see some its an infestation.
:oops: Didn't think about not being able to see it--good point. Should I brush the whole pool with a wire bush at the end of this, or is that not necessary?
 

thephatp

Well-known member
Jul 8, 2018
46
Austin, TX
you should certainly be brushing the entire pool during the slam process
Yeah, I'm definitely brushing the pool. But yesterday, I noticed when I was using the wire brush on the black mold, that some of the "sand" looking stuff on the bottom (mustard algae is what I've guess this is), came up. I wasn't able to brush that off with just a regular brush.

So, my question was actually should I be using a wire brush instead of a regular brush, during the SLAM specifically. I'm definitely brushing the pool, and I'll continue after the SLAM (with a regular brush). Just wondering if the metal one would be better right now.
 

proavia

LifeTime Supporter
TFP Guide
Feb 6, 2015
1,466
Chandler AZ
You may wish to use the stainless steel brush once or twice on the entire surface just to help break stuff loose. Then change to the regular brush from there on out. After that, use the stainless steel brush for any problem areas.