CYA dropped massively at end of SLAM - Halp!

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A

AU Pete

0
Jun 11, 2017
39
Sydney
Background:

First summer with pool.
Testing with Clear Choice Labs saltwater kit (link).
At the beginning of December too much stabiliser (link) was added (i think i overestimated pool volume) and I ended up with CYA at 90.
That's the start of our summer here so I figured that would drift down over summer.
I maintained FC at around 6-7.

=== January 15 ===
PH 7.4
TA 60
FC 7
CYA 90
SWG running on timer of 6hrs/day at 70%
Water is clear - all looking good.

Went away for a week after this, I think I misjudged percentage needed for SWG.
Came home Jan 23 to FC of 4.
Water was a bit cloudy, and some algae spots.

SLAM commenced Jan 24.

=== January 24 ===
FC 10.5 (ran SWG on boost for a day before finally deciding to SLAM)
PH 7.2 (adjusted down a little with MA before SLAM)
CYA 80
(Shock target was 31 based on CYA 80)

5pm - Added 3.6 litres of liquid chlorine (link) to raise FC to shock level 31.
(Brushing walls few times a day from this point on)

=== January 25 ===
Added a total of 4.45 litres LC throughout day in 7 doses to keep FC at 31

=== January 26 ===
Added a total of 0.9 litres LC during day in 2 doses to keep FC at 31

=== January 27 ===
Added a total 1.95 litres LC during day in 3 doses to keep FC at 31

=== January 28 ===
6am - Added .7 litres LC to keep FC at 31

11am - CYA now testing at 60. Pretty big drop I thought, but I had topped up the pool twice (about an inch each time) due to evaporation and splash out.
New shock level based on that is now FC 24.

4pm - FC was at 25, so no more LC added.

=== January 29 ===
Pool water looking very clear, no more visible algae.
All going good... Was initially thinking maybe just 1 more day of SLAM might be needed before an OCLT test, or perhaps even taking up to Mustard Algae level for 24 hours as I suspected MA - 1 particular spot on a shallow step a day prior had some algae that literally looked quite rich yellow/brown and was a little thick - literally like mustard - it wiped away easily in a cloud with a brush though.

But then, measured... 6am:

FC 24
CYA - Less than 30 ?! Maybe as low as 10-20.

Measured CYA multiple times - hardly any cloudiness at all once reagent added.
Pool water itself is looking very clear.

And then it gets weirder...
Measured CYA of provided STANDARD test kit sample (should be 50ppm) and it was measuring at 100ppm. (link to CCL CYA test kit)

I had 2 seperate batches of the CYA detection reagent (from CCL) - both tested the same.

FC had dropped to 17 by 4pm.
Pump still running 24hrs with SWG at 0% output (as has been right through SLAM).

It was getting late in the day (no direct sun) so I just left it. Figured I'd re-measure in direct sun tomorrow and my readings must have been way off. Very puzzled because they were off in opposite directions to what I was expecting.

I'm away from the pool now but will be able to re measure in 7-8 hours (mid afternoon sun).
I'm expecting the FC to drop quite a bit obviously today if CYA is really that low - its a sunny summers day here.

Any ideas how the CYA could have dropped that much so suddenly?
It has freaked me out a bit, didn't get much sleep last night.
I'm worried about high FC levels and damaging the fibreglass/gel pool coating if the CYA is really that low.
Also worried about misreading results and adding too much stabiliser (link) again.

Any advice appreciated,
Pete (in Sydney, AU)
 
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Put a call into Clear Chose Labs. I have read someone else had "bad" CYA regents. I wonder if they had a batch or two go wrong. Give them a call and let us know what they say so we can learn with you please.
 
I'm worried about high FC levels and damaging the fibreglass/gel pool coating if the CYA is really that low.
Click to expand...

I would not be concerned with that. Not that high of FC and fiberglass is impervious to it. Other plastic parts (skimmer, pump, etc) would have issues first.
 
mknauss said:
I would not be concerned with that. Not that high of FC and fiberglass is impervious to it.
Click to expand...

Ok - good to know. Those mentions of "never let your FC go above 3 or you void your warranty" from the manufacturer lurk in the back of my mind (even though I know/trust they are years behind on actual science and don't acknowledge the FC/CYA relationship)

JamesW said:
When the water was cloudy, did the water have a fishy or weird smell?
Click to expand...

no - the only smell i've ever noticed is a slight straight chlorine/clean smell. Pretty sure that was only after I started the SLAM though - not before
 
Hi Pete! :wave: After reading your thread, yeah, the large CYA drop is odd, so I can understand why you would be concerned. Generally we see a large CYA drop due to one of 3 reason:
1. Testing error (to include bad reagent)
2. Large exchange of water (not always on purposes; example - water leak with autofill)
3. FC/CYA converted to ammonia; but that is usually not that common and typically found in pools opening in the spring that sat all winter

Of course a small amount of CYA is consumed each month just through chemical processing, but that's usually limited to about 3-5 ppm or so. There is also the +/- 15% testing variance as well. If anything else was ever added to the water that could explain this oddity, let us know. At least you're vigilant and keeping a close eye on things. :goodjob:
 
I only have a few SLAMs under my belt, but the most recent I had to bump the FC way up because I knew I couldn't get back soon enough for the next top-up. The whole SLAM in that case dropped the CYA by 10 or 15. I chalked it up to CYA being broken down by the excessive FC. It's not a big drop like yours though, so you have to wonder about testing.

In any case, you'll need to get your CYA above 50, so hopefully some new reagent or further tests do the trick. It's definitely helpful to always test CYA under similar lighting conditions, and avoid wrapping your fingers around the viewing tube. The largest error I've noticed here at TFP was the result of clutching the tube in a way that hardly any light could get in.

Even 20 ppm CYA softens the chlorine, but I bet you're around 50 ppm CYA when you get the testing sorted. Good job annihilating the algae!
 
I've had the same low reading problem using clear choice labs CYA reagent, although I was reading very low for both the pool and the reference standard. I'm not sure what fixed the problem, it was one of:
* Repeating test ? Lighting
* Rinsing everything very well
* Shaking CYA reagent (not sure whether anything can come out of solution)

I also have had unexpectedly large falls in CYA although not too the same degree as you and over a longer period of time. I think I did do a slam though. Never came to a satisfactory solution, but has been stable since.

Hope this helps, from another au Pete (Melbourne)
 
Thanks all, an update:

Jan 30: I rinsed everything really well and redid the CYA tests with some bright sunlight - tried sun in front, sun in back, under cover, fingers not obscuring light, the results were actually pretty consistent in all light after thorough mixing and retesting 3 times at 4pm:

Pool CYA: Estimate between 20-30
Reference Standard CYA: Estimate well above 100
FC: 11.5
CC: 0
PH: 7.4
Water: Very clear

Before doing anything else I then made a visit to my local pool store, which of course, I've been enjoying not having to visit.
All I told them was I was getting some weird CYA results and I wanted them to test just CYA. I didn't give them a hint of what my results were.
Their estimate?
Pool CYA: 25
I didn't get them to test the Reference Standard as I'm almost out of it, and wanted to keep it in case I need to send back to CCL (I'll follow this up separately with them).

So at this point I decided to trust that at least my CYA was low - between 20-30, but have not added any stabiliser yet.
Proceeded to do the OCLT test:

At 8:30pm, FC: 10.5
At 6am the next morning, FC: 9.5
I know the test says you pass if the FC went down by "1.0 or less" but I figure I'm right on the edge.

So at this point, I'm taking advantage of my low CYA, and a dark gloomy day here, and SLAMming for 1 more day.
My new SLAM target is only 12 (assuming a CYA of 30) so I only had to put in a small amount of LC to get there.

Water is clearer than it has ever been. I can read the 12pt text on the pool vac brand sticker when its sitting on the bottom in the deep end.
There's no sign of any (visible at least) algae.
Let me know if any of my logic sounds off.

Should I:
a) call it a day if I pass the OCLT test tonight, assume job done and end the SLAM, get the CYA back up and let FC level return to normal?
b) leave CYA where it is and bring the FC up to mustard algae levels just in case for 24 hours (MA target is only 19)?
c) raise the CYA back up to a respectable level between 60-80 and then raise the FC to mustard levels?
 

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thanks,
sorry - meant to reply to this one too...
Texas Splash said:
If anything else was ever added to the water that could explain this oddity, let us know.
Click to expand...

Nothing else added.
We had some people swimming for a few hours during shock level. There might have been a few pellets of possum poo from surrounding trees that were vac'd out within 12 hours. I did backwash the sand filter during the SLAM for a few mins even though the pressure was not that great - there was some murky looking water that came out during the first 30 seconds. (It had been 6 weeks since stabiliser had previously been added). The water was topped up a few inches from the garden hose. Our tap water here in the Northern Beaches of Sydney is pretty excellent quality.

Actually - There's a Privet (NSW WeedWise Info) in our neighbours backyard that has been flowering and dropping its stuff into our tiles area/pool over the last few weeks - it overhangs our fence a little. I hose off the tiles (pushing the litter out onto the grass rather than into the pool) and vac up anything landing in the pool pretty regularly. The remnants of the flowers are small and some likely make it passed the baskets and into the filter though. It's a recognised pest here. That's maybe something?

But I'm not sure - something seemed to happen to that CYA - but I don't know what it was.
 
A yes, your pool is swimmable with your fc up to shock level so your not losing much by staying the course, a successful slam means a clear pool..... forever......

B no, only if you have mustard algae, doesn't sound like you do.

C double no, having the same % of cya/fc ratio is the same on your pool not matter if your cya is 30 or 300.
 
I have found my SWG very helpful at this stage of a SLAM. I only needed to add bleach for the first 2 days then the chlorine from the SWG was more than enough. It made it much easier to avoid chlorine falling too low when I read unable to tend to the pool. I know that opinions vary regarding this on TFP.

*Shock* would a treat strip help with a very rough estimate of CYA?

Until you have decided to end the SLAM don't add CYA. Flowers and pollen consume a lot of chlorine so the privet may be the source of your CH loss.

Edit: spelling
 
GeoQuack said:
*Shock* would a treat strip help with a very rough estimate of CYA?
Click to expand...

test strips? thats the one test (CYA) on test strips that i find is just flat out wrong. the strips i have consistently give a CYA result of about half what a drop based test gives me.
The other tests (FC & PH) seem pretty accurate for me most of the time - but i haven't been using them much now that i know how wrong some of the other results are.
 
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Good to throw an idea out there, but yeh, I find test strips pretty hopeless for CYA, although I find they will give me a yes/no answer as to presence of CYA. Sounds like maybe your CYA standard solution is wonky.

Matt here (JoyfulNoise) makes a good point not to go crazy on the shaking because you can introduce air bubbles into the solution which also intercept light. Inverting it 30 times works perfectly for me, once per second kinda. Just a thought.

I'm for option A as well. The only tweak I'll add is to just go from 25 to 50 ppm CYA until you're confident with the CYA reading.
 
Update: Doh, I failed the OCLT.

At 8pm last night FC: 11.5
At 6am this morning FC: 9.5

Is it possible with my CYA now unusually low (likely in the 20's) that the scale for a OCLT "pass" becomes a bit off?
ie: a couple of pellets of possum poo or a few extra leaves/flowers with pollen might make a dent in my FC pretty easily overnight now right?

Water still super clear.
No sign of visible algae.
 

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