Learning to SLAM

[CKS]

I am just starting my second season as a pool owner and I have been reading around your site extensively. I have also read Pool School. I am so appreciative of the advice given here! I feel like I have finally found a place that offers truly reliable, scientifically-based advice, so thank you!

We bought our current home, with pool, last May. I followed pool store employee advice for my first year. As of last week, I now use only TFP as my guide on all pool issues.

So, I've been trying to get my pool up and running for almost 2 weeks now. Long long long story short, I am now in day 3 of the SLAM process using the recommended test kit and it has been going well. Here are my numbers and pool conditions:

Before starting SLAM:

FC: .39
TC: 2.29
CC: 1.9 (down from 8 earlier last week!)
pH: 7.2
Hardness: 156
Alk: 95
CYA: 53
Copper:0
Iron: .2
Phosphate: over 2283 (after one treatment already - no change)

3 Days into SLAM:
FC: 35
CC:.5
pool water is crystal clear

Here are my questions:
1. I tried OCLT and my FC was 25 at 11:30 last night with CC of 1, 40 minutes after adding 1 gal 8.25% bleach all around pool, as per PoolMath directions. I had to raise it from 17-21. My CC was 0 all day yesterday except for the last test, but we had rain in the evening, so I'm guessing that did it. In-line chlorinator has been empty since closing and there is no way for chlorine to get into my pool, except for that elusive chlorine fairy. Today, FC was 35. User error? Considering I've tested about 15 times in the last 3 days, I don't think it's that as much as 40 minutes wasn't enough time to circulate the bleach. So my main question is, do I have to maintain shock level of 21 all day today and assume I'm not done SLAMming so I can test again tonight? My second question has to do with my FC levels. I'm using PoolMath for all recommended dosages, however my FC rockets up 10-20 ppm over what it is supposed to and I'm not sure why.

2. CYA test: I'm using the pool store CYA results for now because my home CYA testing is not going well. They've been consistent within 5 points or so for the last 2 weeks. Yes, I've taken my water to the pool store 4 times since opening since my test kit wasn't here yet. I waited for the test kit to SLAM. When I did the test of the 50ppm sample, I got a reading of 25. I had my husband read the directions himself and do the test, and he got the same. I tested my pool water and got 35. I'm not sure what is going on there. Any advice?

Thank you so much!

 

[Texas Splash]

Well, one thing for sure ..... you cannot rely on the pool store's CYA test. They test indoor under incandescent lighting which skews the results - among other reasons. The CYA test is absolutely critical to your SLAM since it drives the proper FC level. If you CYA is actually lower like you tested (25-30 or so), then your FC right now is about 2Xs the limit high. SO let's focus on that CYA test. Think about these things:
- Doing the CYA test outside on a bright/sunny day? It must be a bright/clear/sunny day.
- Sun at your back, viewing tube at waist level with body providing shade?
- Your squirt the mixed solution until the black dot completely disappears?
- Once you do that one time, pour the mixed solution back to the mixing bottle and re-do the viewing test as many times as you need to for practice and to get an average reading.

We need to help you with the CYA test before you do anything else.

 

[pooldv]

Welcome to TFP!

Definitely do your own testing and trust your results.

Here are some reference pics for the CYA test, https://www.taylortechnologies.com/ChemistryTopicsCM.ASP?ContentID=36

Some possible causes for FC test issues
Sample size, test error
Pool volume is off
Changing chlorine percentage in Poolmath

 

[CKS]

Thank you both for responding to my questions!

It's a beautiful, sunny day here, so a perfect time to retest CYA. I looked at the images for the test, and I understand how to perform it. I tried the 50ppm sample 4 times in the manner that Texas Splash recommended. I got an average of 40. Could the sample be off a bit? I then tested my pool 4 times and I got an average of about 38. So, I'm guessing I should act on CYA of 38 then, correct?

My pool volume could be off, but I don't think by much. It is not a standard shape, but my husband (who is meticulous about measurements) has done the math, and he says around 20,000. We'll look at it again tonight.

Should I continue the SLAM until I get a more reliable overnight reading?

Thanks so much!

 

[Texas Splash]

We could use of that sunshine in Texas today. Since you tested the pool water and got 38, let's use a CYA of 40. We always round-up or down. That would put your SLAM FC level at 16. So going back to your original questions, I would recommend the following:
- The FC variances are something we need to work out. Just too many fluctuations, and I'm sure it frustrates you as well. Let me just pass-along the basic FC testing routine ..
*** Use a 10ml sample size of pool water, plus one heaping scoop of powder and mix (Barbie pink). Count drops until clear, take that number and divide by 2 (i.e. 14 drops = FC of 7). Always best to let the water mix with pump on for about 30 min prior to testing, and grab water sample from same location each time. You may be doing that already, just want to make sure. Also, do you use a "Speed Stir"?

Since your FC appeared to be a bit over your SLAM level due to the questionable CYA, I would simply maintain an FC of 16 today and do another OCLT tonight. Adjust your bleach at dusk and check FC before bed to ensure it's at 16, but no higher. (Too high can result in excessive loss too). Let's see how that works-out for you.

 

[Mr Bruce]

Two things. First your FC is way over SLAM level Pool School - Chlorine / CYA Chart SLAM level for CYA 40 is 16. I would let it drift down to there and retry OCLT.

2nd, CYA test. Don't stare into the tube, glance quickly down it, and look away, glance, look away. See how the 50ppm standard looks doing that.

e: I swear to god Pat follows me around

 

[pooldv]

The 50ppm sample is not off. Use that sample to "calibrate" your eyes to read the sample as 50 ppm.

 

[Texas Splash]

The 50ppm sample is not off. Use that sample to "calibrate" your eyes to read the sample as 50 ppm.

Oooh, good point! So that would mean if your eyes are seeing the 50 ppm Standard solution as 40 (10 ppm lower), then the same would be true when you looked at the pool water sample. You saw 38, but it was probably 48 - hence a CYA of 50! That would change your SLAM FC to 20 instead of 16. Good call.

 

[CKS]

Ok, thank you for all the insight. Here is where I am now after digesting what you have all said and testing again and yes, love using the SpeedStir:

1. I am now aiming to supersaturate my chlorine test with the 870 powder to thereby eliminate the possibility of not adding enough and skewing my results. I'm aiming for a bit of undissolved solid on the bottom as opposed to no extra powder as I have been getting. Right now, I have a FC of 21.5 and CC of 0 and I have not added anything since last night.

2. Repeated the CYA 50ppm sample with advice given. Solid readings of 40, 42, 40. I can totally see that dot at 50 on a sunny day with the tube at my waist, sun at my back, tube in my shadow, glancing back and forth! I am now out of 50ppm solution, so I'm on my own there. Practicing definitely does help. Could the reagent be off?

3. Tested my own water again and the dot truly disappears around 47. If I stop adding solution at the same mental image of where the 50ppm sample hit the 50 mark, I'm at 55. Shall we say act on CYA of 50? Through this process I've used 53 as my CYA, so it wouldn't change my procedures by much.

4. Chlorine: Based on CYA of 50, I'll maintain FC 20 until I can overnight test again. My pump has been running for almost 2 weeks straight with some breaks in between to backwash. I always test from the same spot each time.

Thank you all so much! Let me know if I should change my plan of attack and I'll keep you posted.

 

[CKS]

9:20 pm update

My husband recalculated our pool volume, and since it is an irregular shape, the best estimate is that our pool holds 18,500 gallons instead of the 20,000 we originally thought.

I retested at 5pm to find FC at 16, CC at 0, CYA dot disappeared at 42, and since I could never get the sample solution dot to disappear at 50ppm, I'm adding a bit to my result and saying CYA 45, splitting the difference and aiming for FC of 18. Pool math calculated 55oz of bleach to bring me up to 18, so I added it at 5pm with brigh sun shining on my pool, unfortunately.

8:30pm: ran the pool robot for a few hours this evening and FC is now at 17.5, CC at .5. I'm going to leave it overnight to see if I pass my OCLT. If my FC is off by .5 from my target, I'm guessing I shouldn't try to tweak it with the chlorine test issues I've been having with my chlorine going so high despite adding the correct amount based on PoolMath. I'll test around 5:30 tomorrow morning.

If there is anything I should do tonight, please let me know.
Thanks again!

 

[Texas Splash]

You're getting the hang of it and the practice is paying off. The only thing I would suggest is to lean towards the higher end of CYA. So if you see 45, round-up to 50. If it's 44 or below, then you can use 40 as the CYA. You get the idea. Then stick with the corresponding SLAM FC level (i.e. 16, 20, 24) and maintain it. We generally don't try to split CYA beyond increments of 10. Maintain the FC and good luck. We'll watch for update tomorrow.

 

[CKS]

5:40 am test results:

I woke up to rain this morning, so I'm not sure if that is playing a role in this or not. I also cut my grass yesterday evening. I use no chemicals on my lawn. Grass does not get tossed directly into my pool when I cut, but I'm sure some flies around and lands in there. So many variables to consider!

FC: 17, CC 1

So I passed the Chlorine retention part, but failed the CC part. Shall I continue to maintain my chlorine level for another day?

 

[duraleigh]

The SLAM is complete when....

1. Your pool water is sparkling and there is no visible algae (dead or alive)

2. Your CC's are .5ppm or less

3. You can hold your FC overnight without losing more than 1ppm.

 

[CKS]

I believe we have SLAM success! My FC held at 17 overnight, CC is 0 and the water is sparkling and perfect. Thank you so much for helping me through this process. I have learned a lot and I'm very appreciative for all of the great advice here!

 

[Texas Splash]

ALRIGHT!