The same outcome can be achieved without water replacement by adding less CYA to begin with, i.e. by using forms of chlorine that don't contain CYA. Then the CYA level won't build up, and this kind of problems will not occur.
Have your water checked for phosphates and nitrates
- Thread starter williamsonpools
- Start date
Also as you said you had high nitrates and high phosphates Your chlorine demand increased In my buisness the more chlorine I am putting in a pool less my money I am making plus the people who do not touch there pool are calling me complaining what's wrong with my pool so in conclusion it is the cause of high nitrates and phosphates that are causing more frequent use of chlorine
I think you might be mixing up higher FC levels with the use of more total chlorine. When you say "chlorine demand" I hear using more total chlorine. Higher CYA levels require higher FC levels, but they do not result in higher total use of chlorine unless you are doing something wrong.
If you look into what is actually happening with the chemistry more carefully, you will find that it isn't actually nitrates/phosphates that are causing the need for additional chlorine. They may be correlated with the fundamental problem (i.e. happen at the same time), but they are not the cause. The underlying cause is nearly always that the CYA level has gone up, but the FC level was not raised enough to compensate. That lowers the active chlorine level below the threshold required to keep algae away, and algae starts growing. At fairly high CYA levels and FC levels that are a little too low for the CYA level you can get into a situation where the water is still clear, but algae is growing in the pool. There is never enough chlorine to kill all of the algae (because too little is being added) but there is enough chlorine to prevent the algae from turning into a full algae bloom. When that happens the chlorine usage goes up until you actually kill the algae.
In 99% of the cases we deal with here it ends up being high CYA levels that cause the problems you are describing. Very occasionally it is something more complex. Only some tiny fraction of those more complex cases end up having even a tangential relationship to nitrates/phosphates, but nitrates/phosphates are never the fundamental cause.
If you look into what is actually happening with the chemistry more carefully, you will find that it isn't actually nitrates/phosphates that are causing the need for additional chlorine. They may be correlated with the fundamental problem (i.e. happen at the same time), but they are not the cause. The underlying cause is nearly always that the CYA level has gone up, but the FC level was not raised enough to compensate. That lowers the active chlorine level below the threshold required to keep algae away, and algae starts growing. At fairly high CYA levels and FC levels that are a little too low for the CYA level you can get into a situation where the water is still clear, but algae is growing in the pool. There is never enough chlorine to kill all of the algae (because too little is being added) but there is enough chlorine to prevent the algae from turning into a full algae bloom. When that happens the chlorine usage goes up until you actually kill the algae.
In 99% of the cases we deal with here it ends up being high CYA levels that cause the problems you are describing. Very occasionally it is something more complex. Only some tiny fraction of those more complex cases end up having even a tangential relationship to nitrates/phosphates, but nitrates/phosphates are never the fundamental cause.
It is true that you need to maintain a certain minimum FC/CYA ratio in order to prevent algae growth in all cases no matter how high the algae nutrient level (phosphate, nitrate) gets. So if your point is that you think the amount of daily chlorine loss at this minimum FC/CYA ratio of 7.5% for non-SWG pools and 5% for SWG pools is too high, then you are right that if you were to lower one of the two algae nutrient levels to much lower levels or if you were to use an algaecide then you could have a lower FC/CYA ratio and not get algae growth.
Between the phosphates and the nitrates, it makes much more sense to lower the phosphates because there are phosphate removers that can help with that. To lower the nitrates, you have to dilute the water, and the nitrates will creep back up over time as the pool is used since chlorine oxidation of ammonia and some nitrogenous organics will produce more nitrate. The phosphates will generally only creep back up if there are phosphates in fill water (especially if you have evaporation from not using a pool cover) or if you use a phosphate-based metal sequenstrant (e.g. HEDP) or if there is a lot of blown-in fertilizer. If you were to let a pool go and have the chlorine get to near zero, then bacteria could grow and convert any organic phosphates in the pool into orthophosphate that algae can then use more quickly for their growth (phosphate removers only remove orthophosphate, not organic phosphate).
So if you were to lower the phosphate level to 100 ppb or were to use a supplemental algaecide, then you could have a lower FC/CYA ratio, such as 3%, and that would use about half as much chlorine daily. However, at the normal 7.5% or 5% FC/CYA level, the daily chlorine demand with a pool in sunlight is roughly 2 ppm FC per day. Do you consider that too high? You'd have to compare the cost of getting to and maintaining a low phosphate level (or using a weekly algaecide) against the savings in using less chlorine.
If you are using Trichlor tabs as your source of chlorine, then for every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm. At 2 ppm FC per day, that's 36 ppm CYA per month; at 1 ppm FC per day it's still 18 ppm CYA per month. So the CYA rises and if you don't raise your FC target proportionally then the FC/CYA ratio drops and algae can then grow (if there are sufficient algae nutrients present). You may think that if you raised the FC level when the CYA level rose that you would use more chlorine, but in fact you end up using less because 1) the active chlorine level is the same so that part lost to sunlight and rate of oxidizing organics (including pool covers) is the same and 2) the higher CYA level may have some shielding effect protecting lower depths from chlorine degradation from sunlight.
So what people do following the TFP method on this forum is use mostly chlorinating liquid or bleach to prevent the CYA from climbing and if they do have CYA climb because they are using Trichlor or Dichlor (for whatever reason) they make sure to raise the FC to keep the FC/CYA ratio at least at the required minimum per the Chlorine / CYA Chart. Now as a pool service, you may be in a different situation where you don't visit the pool frequently enough to maintain the chlorine level without using Trichlor tabs. In that case with the CYA rising and with a desire to minimize chlorine costs you could use supplemental algae prevention (phosphate remover or algaecide), but this is a cost tradeoff you'd have to make. For homeowners who can simply add some chlorinating liquid or bleach to their pool every day or two, they don't have to add anything extra. If someone wants to, they can of course because it's their pool, but we tell them that they don't have to.
This topic regarding the difference between a pool service vs. a pool owner managing their own pool has come up before numerous times. I wrote in this post what some pool services I know have done and the thread The Dark Side goes into more detail about how some pool store methods seem to work, until they don't, and how some pool services operate.
Between the phosphates and the nitrates, it makes much more sense to lower the phosphates because there are phosphate removers that can help with that. To lower the nitrates, you have to dilute the water, and the nitrates will creep back up over time as the pool is used since chlorine oxidation of ammonia and some nitrogenous organics will produce more nitrate. The phosphates will generally only creep back up if there are phosphates in fill water (especially if you have evaporation from not using a pool cover) or if you use a phosphate-based metal sequenstrant (e.g. HEDP) or if there is a lot of blown-in fertilizer. If you were to let a pool go and have the chlorine get to near zero, then bacteria could grow and convert any organic phosphates in the pool into orthophosphate that algae can then use more quickly for their growth (phosphate removers only remove orthophosphate, not organic phosphate).
So if you were to lower the phosphate level to 100 ppb or were to use a supplemental algaecide, then you could have a lower FC/CYA ratio, such as 3%, and that would use about half as much chlorine daily. However, at the normal 7.5% or 5% FC/CYA level, the daily chlorine demand with a pool in sunlight is roughly 2 ppm FC per day. Do you consider that too high? You'd have to compare the cost of getting to and maintaining a low phosphate level (or using a weekly algaecide) against the savings in using less chlorine.
If you are using Trichlor tabs as your source of chlorine, then for every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm. At 2 ppm FC per day, that's 36 ppm CYA per month; at 1 ppm FC per day it's still 18 ppm CYA per month. So the CYA rises and if you don't raise your FC target proportionally then the FC/CYA ratio drops and algae can then grow (if there are sufficient algae nutrients present). You may think that if you raised the FC level when the CYA level rose that you would use more chlorine, but in fact you end up using less because 1) the active chlorine level is the same so that part lost to sunlight and rate of oxidizing organics (including pool covers) is the same and 2) the higher CYA level may have some shielding effect protecting lower depths from chlorine degradation from sunlight.
So what people do following the TFP method on this forum is use mostly chlorinating liquid or bleach to prevent the CYA from climbing and if they do have CYA climb because they are using Trichlor or Dichlor (for whatever reason) they make sure to raise the FC to keep the FC/CYA ratio at least at the required minimum per the Chlorine / CYA Chart. Now as a pool service, you may be in a different situation where you don't visit the pool frequently enough to maintain the chlorine level without using Trichlor tabs. In that case with the CYA rising and with a desire to minimize chlorine costs you could use supplemental algae prevention (phosphate remover or algaecide), but this is a cost tradeoff you'd have to make. For homeowners who can simply add some chlorinating liquid or bleach to their pool every day or two, they don't have to add anything extra. If someone wants to, they can of course because it's their pool, but we tell them that they don't have to.
This topic regarding the difference between a pool service vs. a pool owner managing their own pool has come up before numerous times. I wrote in this post what some pool services I know have done and the thread The Dark Side goes into more detail about how some pool store methods seem to work, until they don't, and how some pool services operate.
Thanks Chemgeek for the info now that I think about it with cya getting high with using pucks and granular shock where I live we close the pools so we have to lower water about 8 inches below tile line (mesh cover) before the cya would get out of the ideal level range
swoopman
0
I can say from experience that winter closing and lowering of the water level is not sufficient to prevent high cya levels. It may delay it more than in other areas but it is not enough of a water exchange to prevent it.
Also, if the pucks are placed in the strainer basket it will cause pipe damage. Here's a pic of an example:
http://www.apcopools.com/galleries/miscellaneous/#viewimage-115
I have chlorinators on most of my pools if not I use a floater prevent the chlorine from damaging my skimmer line at the 90