CYA still high after dumping water

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PMac2

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Dec 20, 2018
6
New Zealand
Hi all,

Obviously I'm new here and very glad to have discovered this site....thanks in advance for any helpful hints and advice.

Anyway, I've been using a "valet" service for several years now, once a month they come and test the water and leave the chemicals with dosing procedure...mainly trichlor tabs, dichlor bags (300gm @ 56%) for shock and the odd hardness and alkalinity increaser.

The main reason I use this service is because I travel a lot for work and have house sitters in to look after the house and cat.

Recently though I noticed a lot of algae forming, I would scrub it off but it would come back very quickly. I looked at the "chem level" results the company leaves each month and everything was in the ideal zone but thought something was odd so went and got the water tested at 2 different pool shops.
Both came back with levels as below
FC 0.2
pH 6.4
Alk 11
CYA 175

Clearly very different to the valet service results (plus a litmus test confirmed).

So based on information garnered from here regarding cya levels and chlorine efficacy and along with both pool shop recommendations I decided to dump 75% of the water and refill (It would have been somewhere between 60-75% from eye).
I have since done that (5 days ago) and following a new test today, cya is still high at about 127 - 145 depending upon which shop test to work off. Litmus test confirms its approx this.
Why would the level not drop more as per the dilution, I was thinking it would be more around the 70-80 mark

One person has said that the cya sits on top of the pool and I pumped out with a submersible pump from the bottom, another said cya is like oil in the water and separates as you "push" on the water but that doesn't make sense to me. I thought it dissolved so no matter where you took the water sample from, the cya would be roughly constant...is one of these correct?
The valet guy said he doesn't believe that cya has any effect on required chlorine levels etc...when I pushed him for a "based on what", he said his experience.

Am I missing something here.

Today's results are and I've just added Ph decreaser and will add liquid chlorine in a few hours.

FC 0.8
pH 7.8
Alk 103
cya as per above

Thanks for any wisdom...
Phil
 
Hello over there! Nice to see you here.

I have an idea why you did not see as much change as you thought you would with the water exchange. Your CYA may have been higher than you thought it was. Most test only test up to 100. The only way to test higher is to do it half and half with non-pool water and double the number. Of course this changes the accuracy of the test so that could cause some mis-reading as well.

I suggest you do another water exchange and see what happens then.

While you are doing that you can also see what GOOD test kit you can get for your pool AND check into getting a SWG as seen here:
Pool School - Salt Water Chlorine Generators This will allow your a lot more freedom with your pool care.

Kim:kim:
 
Welcome to TFP.

PMac2 said:
Both came back with levels as below
FC 0.2
pH 6.4
Alk 11
CYA 175

Clearly very different to the valet service results (plus a litmus test confirmed).

So based on information garnered from here regarding cya levels and chlorine efficacy and along with both pool shop recommendations I decided to dump 75% of the water and refill (It would have been somewhere between 60-75% from eye).
I have since done that (5 days ago) and following a new test today, cya is still high at about 127 - 145 depending upon which shop test to work off. Litmus test confirms its approx this.
Why would the level not drop more as per the dilution, I was thinking it would be more around the 70-80 mark
Click to expand...

Most tests cannot accurately test for CYA over 100. Read our testing directions for CYA at Pool School - CYA and note that step 8 says:

If your CYA level is 90 or higher, repeat the test adjusting the procedure as follows:
Fill the mixing bottle to the lower mark with pool water.
Continue filling the mixing bottle to the upper mark with tap water.
Shake briefly to mix.
Pour off half of the contents of the mixing bottle, so it is again filled to the lower mark.
Continue the test normally from step 2, but multiply the final result by two.
Click to expand...

Now if your CYA was over 200 you might get a reading over 90 on the diluted sample and need to dilute that sample and test again.

It looks like your CYA started around 230 or so.

I would take a sample of your water, dilute it by 50%, and test the CYA and see if you get a result of 60 - 70. Then you know you are on the right path.

Note that your pool guy never should have let your pool get to a FC of 0.2. You can get algea at that FC level even with a low CYA.


PMac2 said:
The valet guy said he doesn't believe that cya has any effect on required chlorine levels etc...when I pushed him for a "based on what", he said his experience.

Am I missing something here.

Today's results are and I've just added Ph decreaser and will add liquid chlorine in a few hours.

FC 0.8
pH 7.8
Alk 103
cya as per above

Thanks for any wisdom...
Phil
Click to expand...

You can do what you wish with your valet guy. You can point out TFP resources and see if he is willing to learn.

I suggest you read Pool School - ABCs of Pool Water Chemistry and Trouble Free Pool School. Take a look at [FC/CYA][/FC/CYA] which tells you the FC level to target based on your CYA. We have lots of information for you at Pool School - Table of Contents

The problem with TFPC methods for valet guys is if you rely on Liquid chlorine to sanitize a pool you need to add it every 2 days or so. FC burns off from the sun at 2-3PPM per day. That does not work for a weekly service. Many of us have a Pool School - Salt Water Chlorine Generators to constantly add CL to our pool automatically. A SWG is what you need if you are away often.
 
Welcome to TFP,

Just to add to the already great advice you have been given, I just wanted to add that the test kit we recommend can be shipped from Australia to New Zealand through this place Clearchoicelabs

I also recommend a SWG - which is the perfect companion for the pool owner who has to travel away from home. By the way CYA more or less disperses evenly throughout the pool once added and dissolved. We recommend that you don't backwash your filter for a week after adding CYA but you should be able to get a good reading with a recommended test kit about 24 hours after the addition. If you read some of the links provided by ajw22 you 'll see that we recommend the sock method for adding CYA.
 
Hi all and thanks for your replies and advice.

I did wonder if the levels were so high that the readers couldn't assess it properly except dispelled that notion as the sources I used for testing were all semi expensive electronic testers, one was the LaMotte ColourQ 7 or 9 and the two pool shop versions were the spinning disc type.
Having just read up on them though, it appears that the LaMotte only reads up to 125ppm maximum, but given that the other 2 spin type gave me a reading of 175, is it safe to assume their parameters are much higher....or probably top out at 175!!!
This would explain the cya level still being so high after dumping the water.....I do find it quite disturbing though that the pool shop people (x 2 different businesses, 3 including the ColourQ) wouldn't consider this option or that they don't know the range/parameters their respective testers are capable of.
Are these electronic testers really not that awesome?

And yes I'm doing some extreme study on best swcg to buy as off again with work on the 7th Jan....yikes.
 
aussieta said:
not sure what swg are available in nz
but australian seem completely different to usa
in usa if set to 50%, will run at 100% for half the time and 0% for half the time
in Aus not sure if it is amperage or voltage that is manipulated
but 50% means 50% for the entire run time
Click to expand...

Not for my Chloromatic. 50% means on for 30 mins/hour.
 
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