Not trusting CYA test before SLAM

[nerf]

Hi there -- We've owned a 30,000 gal SWG in-ground pool for about a year now and through a combination of a bad wind and stupidity (mine) now have what is probably mustard algae growing on the walls (the water is clear). ::sigh:: I thought we were draining the pool this winter so I didn't stay totally on top of things -- and then the hubby didn't get the drain & refill set up in time. Pool lesson 1: Stay on top of things. Pool lesson 2: The husband is no longer a decision-maker re: the pool. Pool lesson 3: STAY ON TOP OF THINGS. So, I'm now mired deep in regret, doing pool penance, and getting ready to SLAM the **** out of it starting this weekend.

Anyway, I've read through the forum this past year and have been testing my own water all along with the Taylor K-2006 kit and I have enough recurring issues with the CYA test that I don't trust myself or my readings. I find that test very subjective and hard to read. Am I imagining the black dot....is that a hint of a black dot....wait, is the black dot gone....no, wait, it MIGHT still be there.... You get the picture. On the whole, my CYA was around 60 all last summer and fall -- the consistency of my readings reassured me. Once this winter, I got a reading of 80, then a few weeks later I got 40. Then back to 60. And now I got 40 yesterday and wondered if I messed up, so did it again today and got about 35. We haven't been in the pool (no splashout) and have not drained any significant water. 35-40 seems too low and I don't want to add stabilizer and then get high readings and have to drain water, etc.

With the impending SLAM, I need to have a good read on the CYA to find my FC target for my regular SLAM and then Mustard SLAM.

Current readings:
pH: 7.4
FC: 6 (I've been keeping this on the higher end of normal while waiting to SLAM)
CC: 0 to 0.5
TA: 100 (I'm currently bringing this down -- it was 150 two days ago and I've been adding acid and aerating -- heading to 70 if I can get it there)
CYA: Who the **** knows. Maybe 35. Maybe 40. Maybe more? But why isn't it still 60? Should the fact that I don't UNDERSTAND the reading CHANGE the reading? LOL

So now to the questions:

What causes CYA to drop over time? I keep hearing only draining and splashout, but we've done neither and my CYA readings are way down.

Would you just proceed to SLAM assuming a CYA of 40 and then test again for CYA after the SLAM is done and adjust if it still reads low?

Why, pool universe, do I have so much trouble reading/trusting this CYA test? Is there a better one than what I've got?

And, from the husband: Can we REALLY pull out the pool light to brush for mustard algae without electrocuting ourselves?

Thanks everyone for being here -- this forum and the Pool School have been so helpful -- though I swear I'm only now feeling like I'm getting a handle on the whole pool thing.

Sharon

 

[Smykowski]

Great post!! I chuckled several times...

Here's my best guesses. See what the others have to say.....

What causes CYA to drop over time? I keep hearing only draining and splashout, but we've done neither and my CYA readings are way down. Only water replacement. Temperature can affect the readings, and circulation can affect the readings.

Would you just proceed to SLAM assuming a CYA of 40 and then test again for CYA after the SLAM is done and adjust if it still reads low? 40 makes the most sense. If you had 60 all summer and had any rain over the winter, a reduction would be most likely.

Why, pool universe, do I have so much trouble reading/trusting this CYA test? Is there a better one than what I've got? Nope, that's it. When you do the reading, pour the solution back and fourth a few times. I'll read it three or four times and take the average. You'll get better at it the more you do it. Worst case, you can buy the 50 ppm standard solution so you know what it should look like at 50.

And, from the husband: Can we REALLY pull out the pool light to brush for mustard algae without electrocuting ourselves? I don't have an inground, but from everything I have read, yes.

Thanks everyone for being here -- this forum and the Pool School have been so helpful -- though I swear I'm only now feeling like I'm getting a handle on the whole pool thing.

Sharon

 

[BoDarville]

Welcome to TFP!

What causes CYA to drop over time? I keep hearing only draining and splashout, but we've done neither and my CYA readings are way down.

Draining and splashout are the most common ways that the CYA level drops. Other possible causes include (1) Rainfall over a long period of time (dilutes the water and, if heavy enough, raises the water level forcing some of it to drain out) and (2) A leak. If you are having to top off your pool more often than in the past and have ruled out other environmental factors, this may be an indication of a leak. Another, but less common cause, is bacteria that can consume CYA. We occasionally hear cases of this happening over the winter.

Would you just proceed to SLAM assuming a CYA of 40 and then test again for CYA after the SLAM is done and adjust if it still reads low?

Yes.

Why, pool universe, do I have so much trouble reading/trusting this CYA test? Is there a better one than what I've got?

Lighting is critical for the CYA test. If you haven't already, check out post #8 in this article: Extended Test Kit Directions

And, from the husband: Can we REALLY pull out the pool light to brush for mustard algae without electrocuting ourselves?

Yes, but make sure the breaker is turned off. If you are still not comfortable, I would contact a pool service technician to do this.

 

[frustratedpoolmom]

Yes I'm curious if you are doing the CYA test with all identical testing situations - outdoor, sunny, back to the sun, waist high... temp of the water- any variations of those tests? There are a few variables that could change the reading as you described.

 

[nerf]

First SLAM...a little confused

Topic merged. Please keep everything relating to one project or problem together in one place. The context is very important for us to be able to answer your questions. JasonLion

So, I have what I think is mustard algae (algae in small patches only on walls on shady side). The water was always crystal clear. I began SLAMing on Friday night with the following starting levels:

pH: 7.2
TA: 70
CYA: 40
Took FC to 16 (a little over, actually)

Pool is: 30,000 gal, plaster, SWG, sand filter, pool folk who have seen it say it might be original to house (1960s). We've owned the house/pool a year.

On Friday, knowing that a Mustard SLAM was coming, we had a pro come and remove our broken pool light. The light niche was FILLED with clumpy dirt/soil/etc. that we brushed into the pool. It was shockingly awful. This, of course, gave me slightly cloudy water. I could still see the bottom of the deep end, but not 'sparkling'. The light is still out and we've been brushing the niche along with the whole pool every day. A new light and housing will go in on Thursday.

I've had pool at 16 or above since Friday night. It passed OCLT on Friday and Saturday nights (even after the dirtball additions on Fri) and has had 0 CC all along -- possibly 0.5 once on Saturday. I kept SLAMing just waiting for the water to completely clear. And THEN, I either failed last night's OCLT or have testing error due to sunlight, but from last night 11 p.m. to this morning at 6:15 a.m. (with sunlight hitting about 1/4-1/3 of the pool), I lost 3 ppm. I'm not sure whether that little bit of early-morning sunlight could cause that kind of FC loss (could it??). And if not, why I would fail OCLT now, after two nights of passing.

The water is looking nice and clear today, and the original plan was to go to mustard level (24) today. But should I keep it at regular SLAM and try the OCLT again tomorrow, making sure my butt is out of bed before sunlight hits the pool? Or because I have passed the OCLT twice already, go to mustard level and then do an OCLT at that level tomorrow morning just to be sure?

Also, I've been running the SWG in the daytime only to help keep the FC levels up during the day. Is that okay? Or should I have had that off the whole time? I have been careful to turn it off at about sunset, a few hours before my last water test for the night.

Thank you all for being here -- I love this forum, and taking care of my own pool with minimal junk from the pool store. This is the first time I've had to shock or SLAM the pool, and it's my own fault for slacking over the winter. And I have learned that lesson the hard way. LOL Never again.

 

[Butterfly]

...... But should I keep it at regular SLAM and try the OCLT again tomorrow, making sure my butt is out of bed before sunlight hits the pool?

That is what I suggest

Also, I've been running the SWG in the daytime only to help keep the FC levels up during the day. Is that okay? Or should I have had that off the whole time?

It is fine to run the SWG to help maintain SLAM levels.

I have been careful to turn it off at about sunset, a few hours before my last water test for the night.

 

[nerf]

Thanks! That's what I'll do.

(And thanks JasonLion for moving the post! Sorry and I'll do that in the future.)