CYA: What's it good for?

[DaveC]

I've been lurking on the forum for a short while gathering a bit of information to help me now that I fired my (worthless) pool guy.

I'll give a bio of myself and my pool in another post, but for now I'd like to know why any amount of cyanuric acid is needed.

If my understanding is correct, CYA combines with FC to prevent FC from being degraded by photochemical reaction due to sunlight. However, by bonding with FC, CYA effectively reduces the amount of FC that's available to do its job killing bacteria and algae. I've not read anywhere how the CYA+Cl bond can be broken, thereby releasing (Free) Cl back into the water. It just seems like CYA is a "chlorine sponge" that only soaks up chlorine, but doesn't release it.

If this is the case, aren't we just as well off totally avoiding products with CYA and just add straight up chlorine as needed to replenish what has been consumed by sunlight and chemical reaction with the stuff it's supposed to kill?

 

[Bama Rambler]

You need to read a little bit more. The chlorine/CYA bond is easily broken. When chlorine gets used up, more is released into the water to do the work. If the CYA never released the FC, you could never get to zero chlorine in a pool with CYA in it, when in fact, it's easy to get to zero chlorine.

You can run a pool with zero CYA, in fact some jurisdictions don't allow CYA in public pools at all. The problem is the amount of FC you lose to sunlight. You would have to constantly add chlorine to make up for that lost by sunlight.

 

[Richard320]

As a late-night snack...as a topping for ice cream... mixed with sour cream for a zesty dip... just kidding. Don't eat the cyanuric acid.

Consider it sunscreen. If you wear sunscreen, it's no guarantee the sun won't fry you, but you'll last a lot longer before it does.

 

[chem geek]

I've not read anywhere how the CYA+Cl bond can be broken, thereby releasing (Free) Cl back into the water. It just seems like CYA is a "chlorine sponge" that only soaks up chlorine, but doesn't release it.

Welcome to TFP!

Without CYA in the water, about half of the FC level will be degraded in an hour in direct noontime sun. The chemical bond is not a strong one and instead there is an equilibrium between chlorine being bound to CYA and unbound chlorine, though most of it is bound. Chlorine is released from CYA fast enough to get completely measured in the FC test. Technical details are in this post with shorter explanations in this post and this post.

 

[DaveC]

Okay, I continued to use tablets in my floater and using Chlor Brite powder to maintain my pool's chlorine level. Now my CYA is right at 50ppm.

To prevent CYA from going too high, I have started using Sodium Hypoclorite (liquid chlorine bleach).

Based upon what I've read and learned:

Sodium Hypoclorite raises pH, so I'll periodically need to add

Muriatic Acid to maintain proper pH. However. . .

Muriatic Acid also lowers Total Alkalinity, so I'll periodically need to add . . .

Sodium Bicarbonate (baking soda) to maintain proper TA.

Bottom line, is it correct to understand that I'll need to routinely add bleach to kill bacteria and algae, muriatic acid to lower the pH raised by the bleach, and baking soda to increase the total alkalinity lowered by the muriatic acid?

 

[Bama Rambler]

When you add bleach it raises pH but when it gets used up it lowers the pH so adding bleach is basically a pH neutral event. I have to add about a cup or two of acid to my pool every other month and the pH stays right at 7.5.

Muriatic acid does lower the pH and the TA but what tends to happen is that eventually things get into equilibrium and the pH becomes stable and therefore so does the TA.

Bottom line is that you will have to add bleach but you may not have to add very much acid and you may not ever have to add baking soda.

One thing you will nedd is a good test kit if you don't already have one so you will know exactly what to add and when you need to add it.

 

[RobbieH]

Very few people get TA so low they have to do anything about it. It's usually the other way around.

I have never put any baking soda in my pool at all, ever. I add MA about once or twice a month, though. Usually around a quart to half gallon each time, depends on if I wait a month or 2 weeks to add. Consider the size of my pool too, you can cut my additions in half for a pool the size of yours.

 

[X-PertPool]

In just my personal experience when pool owners have not used CYA the liners are usually very bleached out (and sometimes have algae). I'm assuming this is because they are using a lot of chlorine because of the sun breaking it down and then when they finally kill off all the algae the chlorine level is usually high enough to start damaging the ink on the vinyl leaving splotches of light patches. I'm basing this off of something I think chem geek wrote about when there is absolutely no CYA relatively low levels of chlorine are a lot stronger.

 

[chem geek]

I'm basing this off of something I think chem geek wrote about when there is absolutely no CYA relatively low levels of chlorine are a lot stronger.

Yup. Even 3 ppm FC with no CYA is about 30 times stronger than our usual FC that is 10% of the CYA level.

 

[DaveC]

My CYA is spot on at 50ppm, so I don't want to continue using Chlor-Brite or Tri-Chlor or anything that will continue adding CYA.

I'm adding about a gallon of 6% liquid bleach each week to keep the available chlorine in the 3-4 ppm range.

My pH continually creeps up into the 7.8 - 8.0 range, so over the course of the past eight weeks I've added 6 gallons of muriatic acid just to keep the pH down in the 7.2-7.6 range.

The acid finally began lowering my Total Alkalinity below 80ppm, so over the past four weeks I've added 16 pounds of baking soda just to keep the TA at or barely above 80ppm.

Could this be a Calcium Hardness issue?

 

[Richard320]

Dave, do you have any scale?

I've been keeping my TA way low, and pH still climbs, and I think it's the calcium carbonate dissolving from the wall and floors. At least I hope so - my whole intention running TA about 50 is to keep CSI in the negatives. I have super high CH, and I bet you do too, since you're not all that far from me as the crow flies.

I probably use 1/2 gallon of Muriatic acid a week. I don't track it all that close.

 

[dmanb2b]

If you let your TA come down to 70 or even 60, your PH rise should slow considerably

 

[monzttr]

My CYA is currently 119 (according to ColorQ7). Based on the calculator I am supposed to keep my FC at 8 - 13 PPM, but in reality its been anywhere from 4 -6.

I have two questions:
1. Is my pool not safe to swim in with a CYA of ~100+ and a FC between 4-6?
2. Would it be best to drain part of my pool to bring the CYA down?

More Info:
Dry heat in Summer (Central California). Consistent mid to high 90's.
Pool size 14,5xx gallons

I think the pool company gave me too much stabilizer, the pool was filled for the first time in April.

Thanks!

 

[linen]

1. Is my pool not safe to swim in with a CYA of ~100+ and a FC between 4-6?

You can do a OLCT to see if you have any organics consuming FC. See: http://www.troublefreepool.com/pool-school/overnight_fc_test, when the sun goes down tonight, I would raise your FC up to 15 ppm (i got 15 from the high normal level calculated by pool calculator for 119 ppm CYA) then test at least 1 hour after and again in the morning before the sun is on your pool.

2. Would it be best to drain part of my pool to bring the CYA down?

I am not sure the color q is very accurate and I am pretty sure most CYA tests are not accurate above 100 ppm, so your CYA concentration might be significantly higher. At 119 your FC needs to be 9 minimum, but again you might need to be much higher than that. I would guess it is just a matter of time until you have a problem.

 

[Optica]

Not familiar with the colorQ7 testing accuracy for CYA, maybe get a 2nd opinion from pool store testing your water or friend with a Taylor or TF100 test kit.

If it is truly at 100+, I would drain and refill to get to ~45-50ppm. Use the pool calculator based on your best test results for CYA level to get the % of drain and refill needed to get back to 50ppm.

As far as it being safe to swim now at your low FC levels, first I would add enough liquid chlorine bleach to get up to the recommended levels. Check your CC levels. CC levels above 0.5 indicate the chlorine is fighting something in the pool. Maybe wait one day and retest. I'm sure it would be ok to swim if water looks clear and tests do not indicate problems. We swim in ponds and lakes all the time with no problems but use your own comfort level to decide.

 

[linen]

As far as it being safe to swim now at your low FC levels, first I would add enough liquid chlorine bleach to get up to the recommended levels. Check your CC levels. CC levels above 0.5 indicate the chlorine is fighting something in the pool. Maybe wait one day and retest. I'm sure it would be ok to swim if water looks clear and tests do not indicate problems. We swim in ponds and lakes all the time with no problems but use your own comfort level to decide.

Good point by Optica here, you do not have to wait to do the OCLT to determine if you are fighting something. However, since your FC level is so low (for the high CYA), CC may not show up since there is not a lot of chlorine available for breaking down the potential organisms. Bottom line if you see CC above 0.5 ppm and/or you fail the OCLT, you need to shock (see link in my sig).

 

[monzttr]

Thanks for the info guys. I think I will drain 50% of my water and add new water to lower the CYA.

 

[linen]

Thanks for the info guys. I think I will drain 50% of my water and add new water to lower the CYA.

Again, I am not sure of the colorq accuracy, but before you drain, I would try to get a good CYA value (look at my sig for test kit recommendations). If you desperate, I think most walmarts have the 6 way HTH that includes the CYA test (you can only do it a couple times with the volume of chems they include). You may need to do a dilution like 1/2 pool water, 1/2 tap water (or better yet distilled) to get the CYA in range of the test.

I did find a post:http://www.troublefreepool.com/colorq-vs-tf-100-accuracy-t33461.html?hilit=colorq cya accuracy, some people have had fairly close results with th TF-100 kit. You could try the dilution method with the colorq i guess.

Edit: this post http://www.troublefreepool.com/lamotte-color-q-t32781.html?hilit=colorq cya accuracy suggests the colorq is not accurate for CYA

 

[frogabog]

Have you been using tablets or powdered shock product? If so, discontinue using those and only use bleach/liquid chlorine. If you drain and refill, and then put more trichlor and dichlor into the pool the CYA level will go back up again.

It's doubtful that the builder added 110ppm of CYA (of course I do not know for sure). They may have put half of that in, but chances are it rose on it's own to the current level due to solid chlorine use.

 

[Ohm_Boy]

CYA: What's it good for?

Huh! Good God y'all.

Anyone else have Edwin Starr singing in their heads when they saw this? Or am I just old?