Do I take CYA into consideration?

[jenner]

In ground pool - 25,000 gallons - 4 years old.

To date little problem with water clarity etc. Noticed my TA is now 160-it is usually around 120. Other readings are as follows:

CL: 10 (kept high due to CYA reading)
PH: 7.6
CYA: approx 100.

I know that an ideal TA is between 100-120. However I have also read that with a high CYA you need to deduct one third to one quarter of your CYA reading from your TA reading to get a true TA level. This would mean my TA is "really" around 130. However even at 160 should I be worrying about it as my water is clear, the PH does not bounce around and I have no algae. The pool shop says I should be putting in 4 pints of muriatic acid for 2 days to lower my TA, but isn't this going to send my PH shooting downwards?

Many thanks for any advise.

[chem geek]

jenner,

Welcome to the pool forum! Though it is technically true that to determine what is called "carbonate alkalinity", you need to subtract 1/3rd of the CYA amount (when the pH is near 7.5) from the TA number, please don't worry about that kind of detail at this point. With calcium carbonate water balance you only need to be in the ballpark while it is your chlorine level, pH and CYA that are much, much more critical.

And yes, you are absolutely correct that adding acid will lower your pH as well as your TA. The correct procedure for lowering TA also involves aeration while holding the pH low (by adding acid) and is described in Ben's Lowering Your Alkalinity procedure, but I would not worry about your TA right now.

With your numbers, the primary problem is the high CYA and it could be higher than 100 depending on how it was measured (if measured visually, then the tube that does such measurements doesn't show marks higher than 100).

Though I will suggest some things you can do, I believe the first thing to do is to get yourself a good test kit if you have not already. If the numbers you reported were from a pool store, then I wouldn't necessarily trust them -- especially the CYA number. You can get a K-2006 test kit from Taylor Technologies rather quickly though more expensively, or you can wait and get a more economical PS-234 kit from Ben at PoolSolutions.

If you did the tests yourself, then getting your CYA down is the main priority. You could just follow Ben's Best Guess CYA chart and keep your FC level above 8 ppm and leave your CYA as it is for now, but you will probably be using a lot of chlorine this way since you can lose up to half in sunlight each day even with high CYA (though this time of year it's probably a lower loss rate). Since it is near the end of the swimming season, you may lose some of your CYA over the winter anyway so you might just want to wait and deal with the CYA issue upon opening in the spring when you "magically" may have less CYA in your pool (we're not certain of the exact reason, but many people have a large loss of CYA over the winter).

If you do want to lower your CYA, then the way to do that is to drain and refill a large portion of your pool with fresh water. You can use the "sheet" method by putting a large sheet over your pool and filling fresh water on top and draining from underneath or you can put in silage tubes and similarly fill the inside with fresh water. A less efficient method that uses more water to dilute is simply to drain from one end of the pool while filling with fresh water at the other. If you live in a place that gets a lot of rain in the winter, then you can use winter rains to fill and overflow your pool to dilute it (that's essentially what I do), but this doesn't work if you live in an area where the water freezes (since you need to lower your water level and shut down your pool, pump, etc. in this case).

When you dilute your CYA, you will automatically dilute (lower) your TA as well. That's another reason not to worry about your TA right now. You will also dilute everything else including your calcium and will need to restore that as well (that's another number that needs to be tested called Calcium Hardness or CH).

You should read about The BBB Method and use liquid chlorine as your primary source of chlorine (unless you have a Salt Water Chlorine Generator - SWCG). I suspect you got to your high CYA levels because of using Tri-Chlor tablets, is that right? If so, stop using them and use liquid chlorine (chlorinating liquid or unscented bleach). If you have an SWCG system, then the manufacturers recommend high CYA levels of around 70-80, but this does not sound like your situation.

By the way, do you have a plaster/gunite pool or a vinyl pool? This makes a difference with regard to whether water balance is important.

If you have any questions or need further clarification, please let us know.

Richard

[jenner]

Many thanks for your advice.

I have a plaster/gunite pool, and yes, I use Triclor tablets. The tablets are 3" and are used via a Pentair automatic cholorine inline feeder. This year I have kept the input valve of the feeder at a pretty low level (around 2) so I have only used 1 large tub of these tablets in the last 12 months. If I have needed to boost the chlorine I have used ordinary bleach poured around directly into the pool.

I have only started to worry about the TA because its only just gone up to 160 - but from your reply I'm beginning to think that maybe I don't need to worry about it too much at this stage??

[chem geek]

Yes, you are correct that you shouldn't worry about the TA nearly as much as the high CYA since the high CYA level is essentially making your chlorine very ineffective. So you have to maintain > 8 ppm chlorine levels until you get your CYA lowered. Technically, your numbers (***uming a Calcium Hardness of 300) give you a saturation index of 0.26 which is not bad (only slightly scaling) so don't worry about the TA.

And to make matters worse, every Tri-Chlor tablet that you use (***uming 8 ounce tablets -- yours may be 6 ounce) adds 2.2 ppm of chlorine but also adds 1.3 ppm of CYA and reduces your pH by 0.03 requiring 4.5 ounces of Soda Ash (Sodium Carbonate or ) or 8.9 ounces of Borax to restore the pH. So you really need to stop using Tri-Chlor tablets and start using liquid chlorine or bleach instead (do not pour liquid chlorine into your feeder or skimmer since it should not mix with the Tri-Chlor directly). You can see how one summer season adding 50 tablets would add 65 ppm of CYA.

I used to use Tri-Chlor tablets myself, in a floating feeder, and after 1-1/2 seasons wound up with CYA over 100 when I had a heck of a time maintaining chlorine levels as the tablets wouldn't dissolve fast enough to give a high enough chlorine level (at least you figured out to use liquid chlorine to supplement). Then I found this site and also investigated pool water chemistry and found that CYA significantly reduces chlorine's effectiveness. A little CYA is good since it helps protect chlorine from breakdown from sunlight, but a lot is not good. I only use liquid chlorine now.

So, bottom line, either ride out this season by maintaining high chlorine levels and hope that the CYA declines over the winter (by the mysterious process we have not yet figured out) or either now or in spring do a drain/refill to reduce the CYA level (which will also reduce TA and CH as well). I ***ume your fill water isn't super-hard water so isn't high in TA and CH. You should probably test your fill water as well so you can predict what will happen when you drain/refill.

Richard

[rawley2]

My CYA is also over 100. I have a fiberglass pool and we are in south Florida with a solar heater so we don't shut down for winter.

I started the summer using one tablet a week and now I'm using about 3 a week. I also use liquid chlorine to shock. Sometimes I use the powered shock but liquid most of the time.

If I'm reading this right I need to drain part of my pool to lower my CYA??

Is that the only way??

Will it hurt to just switch to liquid chlorine until it lowers on it's own. (With all the rain in FL and the way my kids splash this should not take long)

Also what is the best way to avoid this happening again. If I use only liquid chlorine I would be adding it every 2 days in the Florida sun.

Thanks for your help,
Bob Rawley

[Spensar]

You can use liquid until it goes down, just be sure to keep the chlorine levels high enough for that much CYA.

[chem geek]

Bob,

Spensar is correct. You should also keep in mind that usually the CYA level drops over winter closing for reasons that are not yet fully understood. It does seem that CYA slowly degrades, but this seems to get accelerated in a closed pool over the winter. So riding out this season with higher chlorine levels should work fine and then see where you are at come springtime.

Richard

[chem geek]

Bob,

As for the second part of your question on how to avoid the high CYA and the issue of adding liquid chlorine (or bleach) to your pool every 2 days due to the Florida sun, you are correct that even with CYA you will probably lose around half of your FC level during the day due to sunlight. However, a little CYA goes a long way as shown in this graph. Even with 30 ppm CYA you get most of the potential savings and don't need to keep your chlorine level as high -- bottom line, this means you will need to add less chlorine each day (or every other day). On the plus side, you will not need to add base (soda ash; sodium carbonate; borax) frequently -- perhaps not at all.

Though adding chlorine each day or two is the simplest option, there are others as follows:

1) You can get a salt water chlorine generator (SWCG) system. This will use electricity plus salt in your pool (that you add initially) to generate chlorine almost continuously. There is an upfront captial cost, plus a smaller cost for electricity, and a maintenance cost when you need to replace the cell after some number of years.

2) You can get a pool cover that is opaque to UV (most are). This will significantly cut down your chlorine loss and will also save on heating costs (if any).

3) You can get an injection pump for putting liquid chlorine into your pool. This is not common, but there is at least one user on this forum doing this. See this thread, this thread, this thread and this thread.

4) Over the winter, let the rains dilute your pool. That's what I did when I had over 100 ppm CYA due to use of Tri-Chlor when I first got my pool (it only took one and a half seasons to get to 100 ppm CYA).

You are correct that with significant splash-out and with backwashing (if you have a sand or DE filter) you can end up diluting your pool water including its CYA (and TA and CH). You can still use Tri-Chlor in a feeder when you go away on trips (up to about a week) or when you need to add CYA.

Richard

[rawley2]

Bob,


1) You can get a salt water chlorine generator (SWCG) system. This will use electricity plus salt in your pool (that you add initially) to generate chlorine almost continuously. There is an upfront captial cost, plus a smaller cost for electricity, and a maintenance cost when you need to replace the cell after some number of years.

Thanks,

I have been looking for a good reason to switch to salt ever since my neighbor did. With the solar heater we swim in our pool every month. We go a week or so during a cold snap when we don't swim in the winter but that would be about it. Cold snaps in Florida seem to end in 3 days or so.

When I was talking to my neighbor about it he said it was his main reason for going to salt because they also use their pool 12 months a year.

I had a pool guy until 2 months ago but he let it turn green 2 times this summer so I had to let him go and start doing it myself. In other words I'm still learning. I think the salt would make it easier on a rookie like me.


Thanks again for you help all..