Losing at least 2ppm of Chlorine/day

[allen00se]

Hey, related to the topic.. can some of you in this thread post your answers to the following? (I do realize there are other factors at play like Sunshine/Temp/other chemicals)

Pool Size: 20k Gallons
Target FC: 6
Liquid Chloring Strength: 10%
Amt of Chlorine Used Per week: 128oz
CYA level: 15 ppm
Avg FC loss per day: 2ppm



I started using the liquid chlorine method at the end of last year and I am just curious to see some others experiences. I am actually running a homemade pool controller with an ORP sensor so I also want to see if I can get any solid correlation between its readings and the test kit for FC.

 

[jmikeb]

Hey, related to the topic.. can some of you in this thread post your answers to the following? (I do realize there are other factors at play like Sunshine/Temp/other chemicals)

Pool Size: 20k Gallons
Target FC: 6
Liquid Chloring Strength: 10%
Amt of Chlorine Used Per week: 128oz
CYA level: 15 ppm
Avg FC loss per day: 2ppm



I started using the liquid chlorine method at the end of last year and I am just curious to see some others experiences. I am actually running a homemade pool controller with an ORP sensor so I also want to see if I can get any solid correlation between its readings and the test kit for FC.

hello to fellow okie.
i’m a little confused here. 1 gallon of 10% chlorine would raise the fc in your 20k gallon pool by 5ppm. so, if that’s your weekly demand, that’s not close to an fc loss of 2 per day.
also, if my pool had only 15ppm of cya, i would burn off all of my fc on a sunny day

 

[Jimrahbe]

Allen,

We are not at all a fan of ORP systems, but whatever works for you... works for me...

ORP or not, you need to get your CYA up to 30 or 40, which should decrease your FC demand by at least half... Keeping in mind that as the summer gets here your demand will also go up..

Thanks,

Jim R.

 

[Razorhog]

I don't understand. You use a gallon of 10% bleach per week? I use that every other day....

 

[Oly]

The issue I understand from reading past threads on ORP, is that raising CYA above 20ppm will result in incorrect ORP readings. Keeping CYA low enough to not affect the ORP sensor will result in more FC loss from the solar radiation. Round and round you go.

 

[allen00se]

hello to fellow okie.
i’m a little confused here. 1 gallon of 10% chlorine would raise the fc in your 20k gallon pool by 5ppm. so, if that’s your weekly demand, that’s not close to an fc loss of 2 per day.
also, if my pool had only 15ppm of cya, i would burn off all of my fc on a sunny day

Sorry, in my rush to post I left off some important info. Since it is early in the season, not much swimming and no algae, and because I am trying to build up some trend data with my sensor, I have not been maintaining my target FC. I have been dosing the gallon at once and watching to see how fast it burns off and how the FC readings relate to the ORP readings. Also I just drained my pool two weeks ago and went from 100ppm CYA to now around 15ppm so I am still in experimenting mode with the new lower levels of CYA. I know this all makes my numbers look a little like they don't make any sense sorry for the confusion.

The issue I understand from reading past threads on ORP, is that raising CYA above 20ppm will result in incorrect ORP readings. Keeping CYA low enough to not affect the ORP sensor will result in more FC loss from the solar radiation. Round and round you go.

Yes this is why I am running my CYA low, also some papers that I have read in the past spoke to diminishing returns of CYA over that amount anyway (30 ppm of CYA isnt twice as effective as 15 ppm).

 

[mknauss]

also some papers that I have read in the past spoke to diminishing returns of CYA over that amount anyway (30 ppm of CYA isnt twice as effective as 15 ppm).

I suggest your read Pool Water Chemistry

 

[RNeumann]

I don't understand. You use a gallon of 10% bleach per week? I use that every other day....

I am using a gallon of 10% everyday to maintain 6ppm with CYA of 50. I feel like it's pretty excessive especially considering we don't use the pool that often. It is perfectly sparkling clean though!

 

[allen00se]

I suggest your read Pool Water Chemistry

I actually have read over your link, but here is the relevant info from the paper I was referring to from this link Pulsar - The Effect of CYA on Water Balance and Plaster

The effect of CYA on chlorine stabilization is well known and is taught in most pool operator training courses. CYA is used to stabilize chlorine from degradation arising from UV radiation in sunlight. The following graph shows the % chlorine remaining after exposure to sunlight for 1 hr, 2 hr and 3 hr periods.

The graph shows that the effect of CYA is not linear, with the greatest improvement in chlorine retention seen with the first
5 ppm of CYA. Without CYA, only 25% of the chlorine remained after one hour of sunlight exposure. Adding only 5 ppm CYA, chlorine retention increased to 54% after one hour. The retention increased to 65% and 75%, after one hour, for 10 ppm and 20 ppm CYA, respectively. Very little additional benefit was seen by increasing CYA concentrations up to 100 ppm for 1 hr, 2 hr, or 3 hr exposure times.

In order to understand the effect of CYA on disinfection, it is important to understand the chemistry of chlorine and CYA.

 

[Oly]

Go back to Pool Water Chemistry and compare the graph "Chlorine half-life vs CYA at different levels of FC".
This graph has a longer time line, more hours, and higher FC levels that better represent an actual pool water scenario.
Yes much of the FC/CYA response, (3X) is noted for FC levels of 1-3ppm at the 0 to 10ppm CYA but the half-life doubles, (2X) after 3 hours at the 30-40 ppm CYA levels.
As FC levels get above 3ppm then the lower ppm CYA is less effective at increasing the half-life with only 2X or less increase in half-life.
For FC at 5 and 10ppm an increase in CYA ppm has a greater response in protecting the half-life.

The FC half-life continues to improve for all FC levels as CYAppm increases but with diminished returns as CYA gets above 70ppm.

The beauty of self testing is you don't have to only rely on graphs and data, you can in real time, confirm what levels work best for your system.

 

[mknauss]

The following graph shows the % chlorine remaining after exposure to sunlight for 1 hr, 2 hr and 3 hr periods.

At a starting point of 2.5ppm FC. That is too low for any pool with any amount of CYA in it.

 

[Poolzzz]

Personally I don't find either graph that useful because the disinfecting power is not held constant. In other words the amount of "excess" chlorine is constantly changing.

Also, while half life is of some interest because it governs how often we have to add chlorine, we really want total chlorine consumption over time (at a fixed disinfecting rate) and neither graph shows that.

For a desired disinfecting rate one could run with no cya. The price they pay is needing to add CL very frequently (minutes). Or they could increase cya and add CL much less often (hours) but in that case they will be adding much more CL each time. Chemgeek has info showing total consumption is the same over time although he acknowledged anecdotal evidence suggesting otherwise. He speculated as to possible mechanisms but was never able to show a scientific basis for that before he stopped posting.

Note: All this ignores the other big reason for using cya which is for the local buffering effect and the reason Chemgeek recommended always using some cya even for indoor pools.

 

[borjis]

Pool Size: 13k Gallons
Target FC: 6
Liquid Chlorine Strength: 6%
Amt of Chlorine Used Per week: 128oz
CYA level: 50 ppm
Avg FC loss per day: 1ppm if that.

I think why mine barely uses any is that I have the bubble cover on most of the day mon-fri.
on hot days I might swim so the cover is off for maybe 2 hours at most in the evening.

Weekends I usually uncover at 10 or 11am and don't put it back on until 7 or 8pm.

I also keep organic matter / debris out at all times.

 

[mknauss]

And you have cloudy weather much more often than some us ------

 

[Poolzzz]

I'm just north of you with similar usage and am running just under 2 ppm per day when sunny. Maybe peak summer it's a solid 2 ppm on hot sunny days. Depends on how many people are swimming and how long etc. Sun isn't as strong at 49° lat as southern states. Also find pool temp has a big effect...I'm 90+ all the time (95 today! ), at 80 the fc usage is closer to 1ppm. I do have a lot of leaves etc entering the pool daily although not sure that has big effect. Cya lower at 30. Bleak cloudy days usage less than 1 ppm. Lots of variables.