Recommended CYA Level For Sunny Pools

Jump to latest Follow Reply
S

saml

0
Jun 3, 2008
51
Near Knoxville TN
The topic "CYA Discussion" seemed to be open ended. I have converted to the BBB manual method and used 3-3qt jugs of 6% bleach per day when my CYA was at ~90 following a 50% refill (Yes I was in bad shape. Couldn't get PH up or the TA down, and didn't know my chlorine at 3 ppm was useless.) These 3 jugs represents about a 50% loss in FC per day to maintain the min FC per the calculator. I did a 20% drain and refill and am reading something between 65 and 80 before my eyes cross trying to see the dot. Closer to 70 I think which corresponds with the dilution ratio. That results in a lower min FC level and I'm thinking that my bleach usage will go down accordingly. However, before I continue the feed and bleed to get CYA on down to the 40 or so level, what is the recommended CYA level for a 18x36 vinyl pool which is subjected to full sun all day? Also, I think I read in another post somewhere that a 50% loss of FC per day is expected for a sunny pool. Is that right?

Your suggestions have been and continue to be GREATLY appreciated.
 
I am by no means a chemistry expert but I have had some experience running my pool at several different CYA levels. I can tell you that overall, I used less chlorine at higher CYA levels than at lower CYA levels. This is the case even though higher CYA levels required higher FC residuals. So when I doubled the CYA level in the pool, the extinction rate (i.e. CL loss per day) went down by more than half.

For example, at a CYA of 45 ppm, my average extinction rate was 50% with a FC level of 2 ppm so I lost about 1 ppm/day. At a CYA of 80 ppm, my average extinction rate was 10% with a FC level of 4 ppm so I lost about 0.4 ppm/day. My pool is in full sun most of the day.

I have a SWG pool, so I try to target a FC of 5% of the CYA level. BBB pools should be at least 8% of the CYA level according to the CYA chart.

So my opinion is that for most pools, the higher the CYA, the less chlorine that the pool will consume per day but there are other factors which come into play such as organic load. The more stuff that falls into the pool and the more bathers that you have, the less UV extinction matters. So lower CYA levels may allow for better killing power.

Also, higher CYA has it's problems. Not only does the FC level have to be higher, but shock values are higher as well so it is more difficult to kill algae when it occurs. So you really have to decide what is best for you
 
With CYA at 90 you shouldn't be seeing anywhere near a 50% loss per day, even in the sunniest locations. There is very likely something growing in your water and you need to shock.

Higher CYA levels require higher FC levels but use less total chlorine per day.

In very sunny areas with direct sunlight on the pool all day, a CYA level of between 60 and 80 seems to work well.
 
As for something growing I do have a few spots of algea showing up every few days which I sweep away. I had another post on how much algea is OK. I think the answer there is no algea. So the algea could be contributing to the chlorine usage? Looks like it's time for a shock.

Thanks
 
So does that mean that I can safely raise my CYA from 40 to about 70? My pool is in the full sun for about 8 hours each day in Houston. When my CYA was out of control last year (about 150) I had no problems with algae.

Right now I'm feeding the pool about 2.5 quarts of bleach per day. I'm beginning to get strange looks at Wal-Mart - I had 14 boxes of Borax and 3 176oz jugs of Bleach in my cart.
 
  • Like
Reactions: Cinobey
I would say it is fine to raise your CYA to 70 ppm. Even if you kept a minimum of 5.3 ppm or a target of 7 or so ppm, you should find a lower chlorine loss per day. Just make sure you don't let the chlorine drop too much. Since you didn't have algae in the past at high CYA levels, your pool may be low in algae nutrients (phosphates or nitrates), but not every pool is like that.
 
saml said:
As for something growing I do have a few spots of algea showing up every few days which I sweep away. I had another post on how much algea is OK. I think the answer there is no algea. So the algea could be contributing to the chlorine usage? Looks like it's time for a shock.

Thanks
Click to expand...

You have answered your own question. You need to shock your pool with lots of bleach to kill that algae once and for all and keep it going for 48 hours after it's appeared that you have "won" . Until you do, you will struggle. Then you'll need to maintain an FC level that's matched to your CYA level. Go for the high end of the FC range, not the low end as you KNOW you are struggling with algae.

Once you get it clean, start using a weekly maintenance dose of Polyquat 60% to help inhibit the algae growth. You'll notice a dip in FC over the 24 hours after the dose, but just add bleach till it's right again. Polyquat is the only algaecide (other than chlorine) worth using on a regular basis. Stay away from ammonia and copper type algaecides.
 
I just returned from Tucson after attending one day of the Annual Education Conference (AEC) for the National Environmental Health Association (NEHA) where the latest status of the ANSI/APSP-11 standard for "Water Quality in Public Pools and Spas" was presented. I'll write more about that in a separate thread. While I was there, I met with Que Hales of JSPSI who is also the owner of Pool Chlor that services thousands of pools.

Pool Chlor mostly uses gaseous chlorine, though sometimes uses chlorinating liquid as well. Because they service pools in the desert that has very strong sun exposure, their pools all have a CYA level of 100 ppm. They raise the FC level to 14 ppm and one week later when they service the pools again the FC is around 4 ppm (3-5 ppm). Under this pattern, they have a few pools that start to get algae, but from the service person not dosing properly (i.e. not to 14 ppm) and the solution is to set the FC to double (i.e. 28 ppm FC) for one service call. They do not use algaecides (except Borates) or phosphate removers or other chemical treatments except for pH adjustment typically using Borax or Sodium Sesquicarbonate (which is a combination of sodium carbonate and sodium bicarbonate, Na2CO3•NaHCO3•2H2O). They also have around 70 ppm Borates and TA levels of 120-140 ppm. I calculate that adding the chlorine gas going from 4 ppm FC to 14 ppm FC under these conditions would result in a pH drop from 7.5 to 7.3 upon addition, but the usage of chlorine would further drop the pH to 7.18 though carbon dioxide outgassing would offset this during the week.

The 4 ppm FC with 100 ppm CYA is closer to the SWG minimum FC level of 4.5% of the CYA level so I suspect that any nascent algae growth in the last day or two before the next weekly treatment is wiped out by the 14 ppm FC when the chlorine gas is added. Either that or Ben's manual dosing chart is a little conservative to have some leeway for the manual dosing. Also, the high Borates level in the pools maintained by Pool Chlor may help inhibit algae growth to allow this somewhat lower FC level at the end of the weekly chlorine treatment period.

Richard
 
The largest problem with CYA levels of 100 is that it is difficult to distinguish between CYA at 100 and CYA higher than 100 using the common black dot disappearing test. Other than that, the Pool Chlor approach sounds very interesting. I know that several people have reported adding chlorine every other day using CYA levels around 80. Pool Chlor seems to have taken that idea to the extreme.
 
chem geek said:
Either that or Ben's manual dosing chart is a little conservative to have some leeway for the manual dosing.
Click to expand...

Richard--this statement is true. I'm not sure where or when, but it was posted at some point in time that Ben's "Best Guess" table is conservative to prevent someone at the low end (of recommended FC levels for a given CYA range) from getting an infestations--on the principle that they are working pools, not science experiments.
 

Enjoying this content?

Support TFP with a donation.

Give Support
My CYA is roughly 80 (been a while since I tested and I do not have my results sheet handy). My pool is exposed to sun from 10:30 / 11:00 or so until sun-down.

I try to maintain a FC of 9. Prior to installing my LQ I would raise to 12 sometimes and then it would fall back to 7 or so before I brought it back up again. While this may not be the ideal approach (not an expert here, so maybe it is ideal), it worked for my situation and allowed me a few days in between additions.
 
Hi All. I know this is an OLD thread but I have a question. I have recently tested my CYA in my AGP. According to pool math it is a 13,500 gallon pool. My CYA is now 60. My FC is 8 and the chart states a target FC of 6.8 so I am close. My CC is 0. Everything is crystal clear and sparling water. I am in full sun all day! At the beginning of the season I did add 3 trichlor pucks to my chlorinator but they should be all dissolved by now? I have not added anything else other than liquid chlorine (pool Tech). I am not sure where exactly I want to keep my CYA, is 60 a good number for my pool? If so great! If not I might have to drain a little water to bring it down. I have noticed that at 50 and 60 I am losing VERY little Chlorine which is great, but last year I think my CYA was much lower and I was adding bleach daily! SO I just wanted some reassurance.

Thanks!
 
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply