High Chlorine Consumption From Sunlight; Proper CYA Level

[DesertJon74]

Hi,

First-time poster, 6-month reader. Last fall I purchased a used home in the Palm Springs desert area of CA, and knew NOTHING about caring for the pool. Many, many thanks to all here for making me into a pseudo-pool boy. I don't yet know enough to consider myself even competent in pool care, but it's coming slowly through experience and reading the many great posts here.

Anyway, after recently shocking, brushing, and rubbing with trichlor puck to get rid of the start of black algae on the concrete between stone tiles at waterline, I decided to monitor the FC level, perform the overnight FC test, and monitor how long it took for FC to drop.

This area has extreme UV levels and temperature May-Sept.

After shocking (2nd time in 2 days, first time being to peak of ~30 ppm FC):

TF test kit results:

7:30 PM:
FC: 21.5
CC: 0
pH: 7.6
TA: 70
CYA: ~45
CH: not performed

7:00 AM next morning:
FC: 22.5 (went up -- assume due to local currents in pool)

12:30 PM:
FC 14.5

7:00 PM
FC 10.5

12:00 Noon next day:
FC 9.0

As you can see, the FC loss was on the order of 50% the first day, slowing to what looks to be 5-10% loss the second day (I'll test again tonight - but it'll be off since we're swimming today).

For those of you who live in hot, dry, sunny climates, what CYA level works best for you?

I have seen ranges of 40-70 suggested. I am considering slowly bringing my CYA up to 65/70 over the next month with triclor pucks. As a side note, the trichlor pucks in a floater (and this may be my imagination) seemed to do a good job of keeping the black algae off the waterline concrete between the stones.

I assume this b/c until I went to straight clorox I had been using Trichlor floater as well to bring my CYA up, and no significant black algae problems. My "hypothesis" is that the floater bumps along the wall providing localized increased FC that keeps the black algae at bay, as it really seems to prefer the concrete vs the pebble-tec.

 

[257WbyMag]

Welcome to TFP!

I'm not sure how to explain the net gain in FC overnight other than to suggest that the size of the water sample for each of the tests (or the drop size from the testing reagent) were slightly different in each test.

When performing the overnight FC loss test, are you testing first when it's dark and then testing again before the sun hits the water in the morning?

I would repeat the overnight FC loss test and ensure an accurate water sample size by making sure that your water sample meniscus is perfectly aligned with the measurement graduation marks on your tube. Then, when adding drops, wipe the tip of the dropper bottle with a cotton cloth after every couple of drops in order to ensure consistent drop size.

If you are holding your FC overnight and all of the algae is gone, you might consider raising your CYA as you suggested.

 

[DesertJon74]

It's very possible I am off by +/ 0.5 - 1.0 ml. I have also heard stirring between drops (or lack thereof) could make a small difference.

I'm really curious what the philosophy of others is: low CYA with lower FC demand for shock/maintenance, or higher CYA (within reason) and higher FC demand with the intent of slowing down rate of burn-off due to sunlight.

There must be a middle-ground there somewhere. I feel like I'm using a fairly large amount of clorox to maintain FC between 5-10 ppm. I also don't like the idea of having to add clorox every day or even every other day, although I am adapting

My assumption is that the extreme UV exposure is burning of Chlorine at a high rate. But I don't want to increase CYA and therefore FC demand if I'm still going to need to add clorox at same rate. Does anyone have experience with experimenting with CYA levels/overall FC demand/rate of consumption.

 

[257WbyMag]

If your pool is properly maintained, it is very likely that you will never have to shock. Therefore, keeping a lower CYA just to make it easier to shock later isn't really a good choice. You want enough CYA in there that you can make it through the day of swimming an not lose so much FC that you drop below the minimum FC required for your CYA level.

There is no doubt that you are losing some FC to the sun. But until you are algae free, there isn't any reason to raise your CYA higher because this will make it more difficult to shock.

We all have experimented with our CYA levels to find the "sweet spot", so to speak. I don't really doubt that you would benefit from more CYA than you have currently, but you need to make sure that your algae troubles are over first. Black algae can be tough to get rid of. It takes high FC shock levels, LOTS of brushing, accurate testing, and patience. Do this first and then address your CYA levels. Take advantage also of the time that you have when the sun is down since this takes the UV out of the picture.