CYA, Do I really need it?

[NWCanuck]

Here are my numbers first:

FC 4.5 (added 3L two days ago because we have had allot of rain and the pool was only at 2ppm (and I wanted to fill my jugs before the weekend rush)
CC 0
PH 7.6
TA 100
CH 140
CYA <5 (but something there because it is just barely cloudy on the test)
Water Temp 24C

Well I did pickup some CA to add to my pool because I know I am below 10ppm. I have not added any though because I have just a few more questions about it. My pool is 79300L and with a level of CYA 0-10ppm the pool calculator tells me I should be at 1-3ppm FC and shocking to 10ppm.

When I opened the pool on May 12, 2012 the water was clear so I filled the pool and added 10L of 12% Bleach. This was the only time that I shocked the pool because since then I have been able to maintain a FC level between 2-3ppm with minimal effort and have crystal clear water. I have been adding 1.5L (often less ) of bleach every other day when the pool is in use and the cover was off for 8hrs or more. The pool gets 8hrs of direct sun a day with a solar cover on so I thought 1.5 liters of bleach every other day when in use (2 adults and 2 children) was reasonable. I manually vacuum every other day and brush the sides at least once a week. When I use the solar cover I can go 2 or 3 days without the need for adding bleach.

I run the filter at 1500 and shut it off at 2300 every day. The solar cover keeps the water at about 25C while the average outside temperature has been around 22C. I think turning the filter on at 1500 helps mix all that warm surface water from the solar cover into the pool which has help allot with the temperature.

So I guess my question is this. Do I even need to add CYA if my chlorine use is fairly low? I have seen the FC/CYA chart and by adding CYA I am stabilizing my chlorine. But by doing so that stabilized FC is tied up by the CYA and can't oxidize during this period hence why you need to maintain a higher FC level. So this is where I am confused as to the purpose of the CYA. Yeah it stabilizes the FC but I need to have more FC in the water while the stabilized FC is tied up by the CYA? Am I missing something here? :?

Or is my FC use actually considered high and I just don't know it because I am a total NooB!

 

[jblizzle]

We just this discussion today in the second half of this thread:
new-to-this-all-t45999.html

I think you mean FC in the second half of your post and not CH ... calcium hardness has nothing to do with the FC/CYA relationship.

You can get by with low FC BECAUSE your CYA is low. Adding CYA would probably make your daily FC use even lower (although will have less of an affect if you always have a cover).

The CYA just protects the FC ... the FC is still available for sanitation. Yes the FC levels are higher, but the daily FC loss is lower when the CYA is protecting the FC from the sun.

 

[Isaac-1]

There are other advantages of having at least some CYA when it comes to available chlorine, and buffering its effects, from what I have read here even at 10-20 ppm CYA is helpful in this regard, the problem with maintaining this low levels is that they are hard to test for and quantify since the common test only goes down to a reading of 20 or 30 ppm depending on which comparison tube you use.

 

[JasonLion]

Another effect is that chlorine breaking down contaminates produces different intermediate breakdown products depending on the CYA level. With CYA at zero some of the more annoying breakdown products are rather common, while with CYA in the water they are much less common and the less harmful kinds are more common.

 

[woodyp]

If what you're doing is working for you--don't fix it if it ain't broke! FC usage looks quite reasonable. I wouldn't fool with less than 30 CYA if you want to increase it.

 

[NWCanuck]

We just this discussion today in the second half of this thread:
new-to-this-all-t45999.html

I think you mean FC in the second half of your post and not CH ... calcium hardness has nothing to do with the FC/CYA relationship.

You can get by with low FC BECAUSE your CYA is low. Adding CYA would probably make your daily FC use even lower (although will have less of an affect if you always have a cover).

The CYA just protects the FC ... the FC is still available for sanitation. Yes the FC levels are higher, but the daily FC loss is lower when the CYA is protecting the FC from the sun.

Oops, I did mean FC and not CH, I edited my previous post to reflect this (sorry). I guess this is where I am getting confused then. You need a higher FC level when using CYA yet most generic instructions with pool kits (even Taylor kits) tell you to maintain 1-3ppm. That is all and well but these numbers don’t take into account your CYA to FC ratio?

Let’s say you have a CYA level of 70ppm. The chart tells you that you should have a min FC level of 5 and a target of 8 with a shock level of 28. This is where I get confused. Generic instructions tell you not to enter the water after shocking until the water has returned to 1-3ppm. Yet if I have a CYA level of 70ppm like in this example then I am in the Algae danger zone if I let it drop to 3ppm? Is it safe to swim in a pool with a FC level of 8 and a CYA of 70? It must be if the chart shows it, but that is the part I am having trouble getting my head around (Swimming in water with such a high FC level).

 

[JasonLion]

CYA dramatically reduces the activity level of the chlorine. The usual 1-3 guideline was written for a CYA level of zero. As soon as there is CYA in the water everything changes and much higher FC levels have far lower active chlorine levels. The remaining chlorine is still there, but bound up with CYA so it doesn't have the effect it otherwise would.

 

[NWCanuck]

CYA dramatically reduces the activity level of the chlorine. The usual 1-3 guideline was written for a CYA level of zero. As soon as there is CYA in the water everything changes and much higher FC levels have far lower active chlorine levels. The remaining chlorine is still there, but bound up with CYA so it doesn't have the effect it otherwise would.

Thanks Jason, I should have dug deeper.

I found Chem Geeks response here:

how-much-chlorine-is-too-much-t45170.html

And Jblizzle's link here:

new-to-this-all-t45999.html

Thanks for the quick responses though guys!

 

[NWCanuck]

Taken from the earlier ChemGeek link I refered too, says it all.

When I wrote that "higher active chlorine level without CYA is perhaps a bigger problem", I am referring to the fact that an FC with no CYA at usual levels of at least 1-2 ppm results in faster oxidation of skin, swimsuits and hair and faster corrosion of equipment and faster creation of disinfection by-products (and a greater amount of them, assuming you have other means for removing organic precursors and intermediates such as using ozone or UV). In Europe, DIN 19643 has a target FC range of 0.3 - 0.6 ppm with no ozonator or 0.2 - 0.5 ppm with an ozonator and the reason for such low FC levels is to reduce these side effects, especially disinfection by-products. However, it can be impractical to try and maintain such low FC levels which is why I propose using CYA since it acts as an active chlorine buffer letting you have an ample reserve of chlorine (i.e. FC level) while simultaneously having a reasonably low active chlorine level (roughly half the FC/CYA ratio). You get the best of both worlds -- a higher FC so you don't "run out" of chlorine, even locally, while having the active chlorine level be low to reduce the rate of disinfection by-products and other side effects of chlorine.

I understand now! :idea:

So to get from <5ppm CYA, the pool calculator says that I need to add 2.4kg of CYA. Should I half this dose or should I go for full dose? From what I have read do I put this in a sock and hang it over a return? I just backwashed so now might be the best time to do it.

Thanks again!

 

[JasonLion]

Sure start with 2.4 kg, wait a week, find out where you ended up, and adjust from there if needed.

I would put the CYA in a sock (or stocking) and put the sock in a skimmer (as long as it doesn't completely block the skimmer).

 

[Isaac-1]

That could work for now, the problem is with a target CYA of around 5ppm you will have no way of maintaining that level in the long run since the test don't reliably measure below 20 ppm. Sure you can make a guess that you have some CYA, but less than 20 ppm, the question is then, do you have 5 ppm or 15 ppm? This alone makes 20 ppm a reasonable minimum CYA target level, since you can measure and maintain that level, plus maintain FC at around 3 ppm for a appropriate target level, with a 2 ppm minimum.

 

[NWCanuck]

That could work for now, the problem is with a target CYA of around 5ppm you will have no way of maintaining that level in the long run since the test don't reliably measure below 20 ppm. Sure you can make a guess that you have some CYA, but less than 20 ppm, the question is then, do you have 5 ppm or 15 ppm? This alone makes 20 ppm a reasonable minimum CYA target level, since you can measure and maintain that level, plus maintain FC at around 3 ppm for a appropriate target level, with a 2 ppm minimum.

I hear where you are going with that Isaac. I was coming in with less than 10ppm only because I am able to fill the CYA tube on the Taylor 2006 all the way to the top and still see the black dot at the bottom with some very minor cloudiness. Looking at the tube it stops at 30ppm like you say, without doing the 50:50 dilution to get a true reading I am shooting in the dark. I think you and someone else mentioned how to drill this down to a more exact number in a previous post of mine. I will definitely do this before going full strength on the addition on CYA to the water so I don't over shoot my target of 30ppm to start.

Thanks again for all your help guys.