Crystal clear pool but cant finish SLAM - feeling defeated and overwhelmed!

aam9

Member
Jun 1, 2016
10
Cincinnati, OH
Pool Size
33000
Surface
Vinyl
Chlorine
Liquid Chlorine
Been using TFP methods on our pool since I found you all 8 years ago! Not much has come up that I haven't been able to resolve using forum posts and advice. That is, until recently. Having an issue with our pool that is perplexing me. Opened (mid-May) without any real water chemistry issues and passed OCLT the first night of SLAM. At that point, CYA was sitting at 40 (sometimes could see dot just below 40 mark, sometimes just above), so maintained FC at goal of 7, never allowing it to hit below 4. Looking back, I *think* the offending incident may have happened while we were gone for 2 days at the beginning of June (6/2 - 6/4). I beefed up the FC before we left and told the person watching our pool to add 1 gallon each day (which covers typical FC loss each day). It was incredibly sunny AND hot that weekend, but everything tested in range upon our return. It IS possible, though, it drifted below the recommended minimum while we were gone.

Last Wednesday (6/14) noticed the pool was starting to get cloudy. We had been having issues with our aging filter and rising pressure, so took the filter apart and cleaned it out thinking it could be a filtration issue. Water started to clear up by the end of the day but wasn't the crystal clear we are used to. Woke up 6/15 and water still wasn't completely clear so decided it's possible that the rising pressure and cloudiness was not a filtration thing but a water chemistry thing, and started a SLAM based on CYA of 40 using 10% LC. Woke up 6/16 and water was crystal clear again, but completely surprised to see that CC's were above 1 and failed OCLT. Assumed we had an algae bloom and started brushing (twice daily) and vacuuming (once daily). Pressures haven't risen but did backwash once in case there was algae debris inside. I will post info below, but haven't been able to pass OCLT and CC's range from 1.5-2.5 (usually decrease on hot, sunny days and increase at night). There hasn't been ANY trace of algae debris, no areas of discoloration, no "swooshing" piles of gunk when we sweep, and the DE medium was "normal" color when we back washed. We've removed the ladder, cleaned all pool tools with bleach mixture, and I've toothbrush scrubbed all the nooks and crannies I can get to (daily).

On 6/17 I made the decision to bump the SLAM up to CYA 50 levels since sometimes, when I check CYA, it's right below the 40 marker and maybe I should have been rounding up. What's interesting is that when I was SLAMing to 40 my CC"s were always 1 - 1.5. When I moved to 50, the CC's increased to 2 - 2.5. Obviously something is happening in my pool, as I've never had a SLAM go past 48 hours. My theory is an elusive algae that I can't seem to pinpoint, but hoping I can get some feedback and encouragement. I think I'm at the POP phase but I'm physically, mentally, and financially hitting a wall!

Starting Measurements:
pH - 7.5 (I have a question about this below)
CYA 40; but started dosing based on 50 since sometimes the dot disappeared right below the 40 marker putting it in the 40-50 range
TA - 80
CH - 200

Every time I tested I added enough 10% LC to get me to SLAM level. As you can see sometimes it held until the next sample, most times not.
6/15 5:30p (started SLAM) FC-4.5; CC-0 (had CC's of 0 since opening SLAM, despite recent cloudy water)
7p FC - 17; CC - 0
9p FC-14.5; CC - 1.5
1:45 a (tech 6/16) FC - 16.5; CC - 1.0

6/16 8:00a FC 14.5 (failed OCLT); CC - 1.5
noon FC-16; CC-1.5
2:45p FC-14; CC-1.0
5:45p FC-16; CC-1.0
9:20p FC-16; CC-1.0
11:30p 17.5; CC-1.5 (not sure why FC drifted up since I didn't add anything after 9:20 test)

6/17 8:45 a FC-16 (failed OCLT); CC-1.5
11:45a FC-15; CC-1.5
4:10p FC-12; CC-1.0
6:45p FC-12; CC-1.0 (changed FC target to 20)
8:25p FC-21; CC-2.0 (notice CC increase when I increased FC level)
midnight FC-21; CC-1.0

6/18 (made a concerted effort to test and adjust every 2 hours; sunny and hot day so think I lost quite a bit of FC to sun as pool gets full sun pretty much from 9 am - 7 pm)
6:10a FC-19 (failed OCLT); CC-2.0
9a FC-16; CC-2.0
11a FC-17; CC-1.0
1 pm FC-17; CC-1.5
3p FC-19.5; CC1.0
5p FC-18; CC-1.0
7p FC-20; CC-2.0
9p FC-17; CC-1.5
11:20p FC-22.5; CC-1.5

6/19 (today- overcast, cool, off and on rain)
5:30a FC-18.5 (failed OCLT); CC-2.5
7:45 FC-20.5; CC-2.5
9:35 FC-21; CC-2.5
HOLDING on further additions until get advice about pH

If you have made it this far, you are my hero! Questions:

1. What am I missing? Agree it's algae and just continue doing what I'm doing? Think it might be something else? Suggestions on what else I could be doing? See anything in my testing that stands out to you?
2. When looking through posts trying to troubleshoot, I realized that I was hasty in starting my SLAM and didn't bring my pH down to 7.2. I started at 7.5. Considering my high FC SLAM level, and the fact that I've already put in 20-25 bottles of liquid chlorine, would it be wise for me to try and adjust my pH now or wait until SLAM is done (not knowing how long and how much more LC will be added). If I should adjust now, should I let it drop to 10, test, adjust, and bring back up to SLAM OR add some MA while SLAMing knowing I started at 7.5 and try to bring down a little?
3. Considering my CYA has hovered a bit above and a bit below the 40 marker, is it wise for me to continue to SLAM to CYA 50 or drop back down to CYA 40 levels?

Again, you have my utmost appreciation in advance!
 
Clean your test vials you use for FC testing. Use alcohol or straight bleach. The CC numbers make no sense without you having added some pool store potion.
You can use the SLAM level for CYA of 40.
Do not worry about the pH.

Let us know how it goes.
 
Are you testing in the morning before the sun comes up? I see 8:00 am and 8:45 am. listed We are getting sun on the pool by 7:30 am now.
 
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Clean your test vials you use for FC testing. Use alcohol or straight bleach. The CC numbers make no sense without you having added some pool store potion.
You can use the SLAM level for CYA of 40.
Do not worry about the pH.

Let us know how it goes.
Well, I feel like an idiot! I cleaned the vial and re-tested. FC stayed the same at 21, but CC dropped to a faint 0.5! At this point, FC has been holding since 7:45 this morning. Will let the FC drift to 16 and maintain until I pass the OCLT with a CC of .5 or less.

Thank you so much for your helpful response!!!!
 
Are you testing in the morning before the sun comes up? I see 8:00 am and 8:45 am. listed We are getting sun on the pool by 7:30 am now.
That is a good point, thank you! Yesterday I checked at 6:10 am (lost 2 ppm), and this morning at 5:30 am (lost 4 ppm). Here's hoping the newly cleaned testing vial helps me to pass tonight, otherwise I will continue to check bright and early each morning.
 
Considering my CYA has hovered a bit above and a bit below the 40 marker, is it wise for me to continue to SLAM to CYA 50 or drop back down to CYA 40 levels?
Also, you may want to try this method for reading your CYA as I find it easier and avoids staring at the dot as you pour.

Pour the mixed solution to a known level, say 90, peer in and confirm you can see black dot. Now pour mixed solution to 80 mark, peer in again, if you can still see dot, hold tube up and pour mixed solution to the 70 mark, then peer in again to view dot. Continue this until you are not able to see the dot - then use your CYA number as the value you last saw the dot. This method avoids constantly looking down the tube which can create the illusion of always seeing the dot due to staring down the tube. This also helps that you only report CYA values in decade numbers due to the logarithmic scale of the tube.
 
Also, you may want to try this method for reading your CYA as I find it easier and avoids staring at the dot as you pour.

Pour the mixed solution to a known level, say 90, peer in and confirm you can see black dot. Now pour mixed solution to 80 mark, peer in again, if you can still see dot, hold tube up and pour mixed solution to the 70 mark, then peer in again to view dot. Continue this until you are not able to see the dot - then use your CYA number as the value you last saw the dot. This method avoids constantly looking down the tube which can create the illusion of always seeing the dot due to staring down the tube. This also helps that you only report CYA values in decade numbers due to the logarithmic scale of the tube.
That is a really helpful tip and can see how it would eliminate some of the objectivity of that test. Thank you!
 
Good luck 👍🏻
I couldn’t believe it myself after cleaning my beaker the first time. I wasn’t having cc issues but it had gotten so dark/dingy. It was like having a new beaker! I clean it regularly now. Just one of those things you don’t think of.
 
Good luck 👍🏻
I couldn’t believe it myself after cleaning my beaker the first time. I wasn’t having cc issues but it had gotten so dark/dingy. It was like having a new beaker! I clean it regularly now. Just one of those things you don’t think of.
Thank you! It's such a simple thing that I didn't think of. Here's hoping it makes the difference!
 
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I know you said you checked the nooks & the ladder but I’ll cover all the other common offenders as well:
*Check & scrub every nook & cranny where algae may hide (light niches, steps, drain covers, ladder handrails, skimmer throats/weirs, abandoned lines, autofill, overflow drains, etc.)
*If water can go there, algae can thrive there.
*Run slam level water through all water features & lines for at least a couple hours a day during the SLAM Process.
 
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Just wanted to update: Passed the OCLT! Thank you all for the info, especially about cleaning the vials. Embarrassed that small detail probably cost so much extra time, money, effort, and sanity, but so glad the SLAM is over. Letting it drift now, and waiting to drop below 10 so I can test and adjust pH if necessary. Again, thank you for the insight!
 
Just wanted to update: Passed the OCLT! Thank you all for the info, especially about cleaning the vials. Embarrassed that small detail probably cost so much extra time, money, effort, and sanity, but so glad the SLAM is over. Letting it drift now, and waiting to drop below 10 so I can test and adjust pH if necessary. Again, thank you for the insight!
Congrats. Well Done. We all live and learn. Hopefully your lessons will be read by others and gain that knowledge.
 
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If it's not too late take the slam for another day as insurance. You'd be surprised how many end it day 1 of a good OCLT and then two weeks later they're back to square 1 and do the OCLT again in the morning.
 
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