Stubbornly high CYA...

[JayG]

We inherited a pool maintained on pucks and as this was my first pool, I found TFP in my quest to understand what was involved in pool care and feeding. Last season (shortly after closing on the new property), I bought the TFT kit and measured CYA levels of >100. Not surprising, from what I learned. I figured I take care of it in the Spring.

Last fall, the pool level was lowered about 18" for closing (about 25%) and was "refilled" by winter precipitation almost to the "full" level by March. Thinking I was clever, I put a sump pump onto the 2nd step and drained another 18". I remeasured CYA and other values. The CYA was still 90-100. Granted, the company that closed the pool put in some floating pucks, but I was surprised.

I refilled the pool last week and used the sump pump to recirculate things. Today, I take a new set of chemistries and find CYA still measuring out at 80-90. So, some progress, but nearly as much as I expected. I tried warming the water used for the test and it made no difference. I currently have "SLAM" levels of FC (FC=25; CC=0). Does that influence the reading?

My full test results today:

FC 25
CC 0
pH 7.5
CH 100
TA 100
CYA 90

Anything here that could throw off my CYA test? My leading hypotheses are that either I didn't dilute as much as I thought with our winter precipitation and my draining/refill; or that the original CYA of >100 was much higher than I figured (I didn't do the dilution test); that there was some sort of layering and that what I drained off after winter precipitation was not mixed with the rest; or that something in my other chemistries is throwing off the test.

Thoughts? Suggestions?

Many thanks,

Jay

 

[jblizzle]

The only thing that can influence the CYA test is the water temperature and the lighting used for the test.

My CYA was around 300ppm when I took over. My guess is yours was higher than you thought.

And yes, if you did not circulate the water prior to draining, it could have been stratified.

 

[JayG]

The only thing that can influence the CYA test is the water temperature and the lighting used for the test.

My CYA was around 300ppm when I took over. My guess is yours was higher than you thought.

And yes, if you did not circulate the water prior to draining, it could have been stratified.

Many thanks! You have confirmed at least 2 of my hypotheses as valid. I'm draining more water tonight and now have a Triton plus robot mixing things up. I'm sure I'll get to the bottom of this....

 

[kimkats]

Jay, You are spot on with your thinking. It was higher than you thought, it was not mixed up good, AND with the pucks from closing it went up some (not much but....)

You WILL get it down. I like that you have your cleaner in there to mix things up.

You will LOVE how your pool looks after you get it all balanced. That lower CYA will allow the FC to be more effective so the water will look even better!

Kim

 

[JayG]

Thanks Kim! It's good to know that I'm on the right track.

 

[JayG]

So, I drained about 1/3 of the pool and refilled over the weekend. It seems to be working. CYA is now ~60. Here is the whole testing enchilada:

FC 17.5
CC 0.5
pH 7.2
CH 125
TA 80

Can I live with a CYA of 60? I'm guessing it will go down over the season due to splash out and rain, no? Or should I drop it down some more? Should I worry that my CH went up with the drain/refill? I don't recall that our city water is "hard". When I get back in town, I'll retest.

Before leaving for 3 days, I bumped up the FC to 28. I programmed the robot to run 3 hrs/day in the meantime. Hopefully, I won't have a green pool when I get back. I've never seen any measurable CC before.

Thoughts?

 

[northrn]

You can live with a CYA of 60. Just match your SLAM and maintenance dose of chlorine accordingly. CYA levels lower a couple of ways...you either drain (or splash out) and refill or RO treatment. I would leave it as is.

As for your calcium level, that seems low to me since you have a pebble finish and a heater. I'll leave that to someone with more experience to give advice.

 

[MarianParoo]

Is the water clear? Yup, northrn is right Calcium is low. See this: Pool School - Recommended Levels

 

[JayG]

Thanks for the replies.

Yes, the pool has needed CH since it was closed. I was only surprised that the Ca didn't dilute as much as expected. I already have the CaCl2 waiting to add once I get my CYA problem solved.

The water is still cloudy, but not green. The robot is pulling out what looks like brown silt that probably came through the mesh cover over winter. Again, nothing greenish. The bump up to shock-like levels was an attempt to buy some insurance for the 3 days I'm away. The water is still very cold (~50°F).

Soon, my Stenner will be up and running and will have my equipment pad on line.

 

[JayG]

OK. Maybe I was optimistic regarding my CYA levels. Now, depending on the day, I am measuring 60-80 CYA (I ordered the 50 ppm CYA solution to be sure I'm doing this right). It is certainly no lower than 60 and my guess is that 70 ppm is probably the right measure. Should I do another partial drain and refill before the season starts? Part of me wants to start with a level no higher than 50; another part of me figures that with rain and splash out, it might come down gradually over the season and would certainly be in range for next season (with closing draw down and opening refill).

Northrn indicated I was OK at 60. Does the same apply to somewhat higher levels? Part of me also reasons that the pool lived at a CYA >200 for probably a couple of seasons without major problems. From what I understand, the only risk I'm taking is needing higher levels of chlorine for a SLAM. I have a Stenner for chlorine and can maintain the levels at the appropriate CYA/Cl ratio (so I'm hoping no SLAM will be needed).

Any change to the advice to live with the CYA as is?

Thanks!

 

[duraleigh]

Given your geographic location, I would lower it to 40-50. That said, with the stenner, you can treat it like a salt pool and use salt pool numbers so your CYa would be fine at 60-70.

Costwise, I wouldn't even guess at how little the difference would be in FC use....it wouldn't be much

I just like pools to run CYA down pretty low......they seem more manageable

 

[zea3]

You can live with CYA of 60-70. As long as you dose the pool according to the CYA level you should be fine.

 

[JayG]

Thanks for the advice. Dave, when you say, "with the stenner, you can treat it like a salt pool and use salt pool numbers", do you mean FC of 5-8 (for a NSWG pool) or 3-5 as recommended for a SWG pool? zea seems to indicate that it should be treated like a NSWG pool. Just trying to be sure of what I'm shooting for on my FC.

BTW, I've never understood why the two Cl delivery methods wouldn't require the same CYA/FC ratio.

Thanks again.

 

[jblizzle]

Treat it at a non-SWG pool, just with the higher CYA and FC levels.

The SWG has lower recommended FC levels because the FC is continually added and the level stays much more constant and does not have the large fluctuations or error due to human bleach additions.

 

[JayG]

Thanks for clearing that up. Much appreciated!

 

[JayG]

The SWG has lower recommended FC levels because the FC is continually added and the level stays much more constant and does not have the large fluctuations or error due to human bleach additions.

Took me a bit to process this information, but now I have a follow-up question: if the SWG can maintain more constant FC levels than a human adding bleach (hence requiring lower FC/CYA ratios): does that mean that constant FC addition over 24 hrs is better than a bolus of FC that arrives consistently? I know this has been discussed before (without a clear resolution to my reading), but I assumed that for a Stenner-based FC delivery system, that a consistent, nightly, bolus of FC was preferable to multiple mini boli (more SWG-like). My understanding was that adding a single, predictable, bolus of bleach after sundown with a Stenner would raise FC during the night that would then "decay" to target FC levels by sundown the next day...then rinse and repeat indefinitely unless my FC tests showed an anomaly or if there were reason to boost FC (rain, pool party, etc). I figured that would be best bet for controlling algae growth (like a nightly "mini-shock"). Is there evidence to support that a more constant FC injection by a Stenner over the 24 hr day is preferable?

Apologies if I'm making things more complicated than they should be, but it would help me to know how to program my Stenner: one big nightly bolus vs multiple doses spread over the 24 hr cycle.

Thanks!

Jay

 

[jblizzle]

I have started a response 3 times now and thinking of tangents ... not a straight forward answer ... so here are the points I thought of.

1. The higher the FC level, the more ppm will be lost to the sun. So there is that down side to starting the day with a "high" FC level.

2. Running the pump 24/7 just so that you can add bleach constantly is a waste of $ on power. Generally you want to run the pump as little as possible such that you meet various needs (SWG generation, cleaning, solar, heating, etc). But, there is some minor advantage to splitting up the run time to spread out the skimming and chemical addition.

3. The lower FC recommendations for the SWG may also have something to do with the elevated FC levels that occurs in the SWG cell itself. These lower FC levels are an absolute minimum, while the higher FC levels for non-SWG have some wiggle room (again human in the loop )

 

[JayG]

Thanks Jason. That all makes sense...sort of. I get that having a high FC in the morning will lead to more rapid UV degradation. I get that running a pump 24/7 to add bleach is an added cost, but doesn't the same logic apply to SWG? The first part of your 3rd point also makes sense. The local FC created in the cell is probably different than the higher FC created at the local injection point of a Stenner (I think). I guess it is the last part of point 3 that has me wondering: doesn't the Stenner delivery system take the human out of the loop and reduce the wiggle room? If so, I would think that SWG rules could apply to a Stenner set up.

To be clear, I'm really not trying to pick nits. I understand that pool care is not an exact science and for sure I'm going to abide by the collective wisdom of the TFP in managing my pool. The goal of my first year of managing our family pool is not to make a complete mess (otherwise, my better half would fire me and have me hire the puck brigade again). So I plan to be very conservative on our FC levels to make sure there is no need to SLAM.

I'm just a curious person by temperament. Perhaps, this is specific question is better suited for the "Deep End" or "chemistry 201" as it is rather esoteric and specific to Stenner users. If you feel it is useful, I can pose this specific issue in one of those forums. For now, you have fully addressed my question of how to manage my FC for the upcoming season.

Many thanks,

Jay

 

[JayG]

Just as a follow up. I received my 50 ppm CYA standard solution and indeed, I think I can safely call my CYA at 70. I also added 50 lbs of CaCl2 and raised my CH from 125 to 275. I guess this confirms that I do indeed have a 35,000 gallon pool as PoolMath predicted that 49 lbs would get me from 125 to 275 with that volume. I have 25 lbs of Cal-Hypo that if I add it bit by bit in lieu of bleach can raise my CH another another ~40 ppm. That should be about right for a plaster pool. Thanks again for everyone's help. I love this site.

 

[pooldv]

Nice work!