CYA discrepancy

[brianmcb]

This is my first year with a pool and I ordered the TF-100 kit to try to handle treating the pool myself without dealing with pool stores and their chemicals.

When I opened last Friday, the pool was a swamp (it has a mesh cover). Lots and lots of pollen and debris, and the water was so green and cloudy I could barely see the first step in the shallow end. I've been running my DE filter 24/7, backwashing every 6-12 hours or so (pressure goes up 10 psi after this time) and adding 6 pounds of DE each time. My SWG has been running the whole time. This morning I could actually see the bottom of the deep end so that's a huge improvement. My FC level is at 1ppm.

On Saturday I took some water to a pool store to have it tested, to give myself a baseline. They showed my CYA as being 105 which seemed insane to me, I have not added any CYA. I bought the house in September and have not added any chemicals at all. When I do the CYA test from the TF-100 kit, I essentially get 0 - I can fill up the graduated cylinder and the black dot never fades (basically the solution is clear).

Am I doing something wrong? Was the pool store's CYA test really inaccurate because of how nasty the water was? Can anyone explain what might be happening here? My problem obviously is that I have no idea how to calculate my shock level because I don't know if my CYA is way too low or way too high.

 

[mynewpool]

I would go with your result as the pool store has known to be way off on that cya test. They told me mine was 140 and it was actually 30-40 so no suprise there. 105 seems like an odd number to start with. Do you know how they did the test for CYA?

Also if possible post a full set of results and the pros will be able to get you going in the right direction.

 

[JohnT]

Take a sample of your tap water in and have them test it for you. See what CYA number they get from that.

 

[Butterfly]

Always trust your own test results over pool store. Your CYA is most likely just what you see, zero or too low to measure.

Your shock level is 10 - for now

Just to help you confirm your testing, have you seen the CYA test pics from Taylor? http://www.taylortechnologies.com/Chemi ... ntentID=36

 

[brianmcb]

Do you know how they did the test for CYA?

I'm not sure how they did their tests. It looked to me like they put a test strip into my water sample, then inserted the strip into a machine.

Take a sample of your tap water in and have them test it for you. See what CYA number they get from that.

I'll do that, I'm guessing CYA in tap water is 0 so it will tell me if their machine is reading it wrong?

Always trust your own test results over pool store. Your CYA is most likely just what you see, zero or too low to measure.

Your shock level is 10 - for now

Just to help you confirm your testing, have you seen the CYA test pics from Taylor? http://www.taylortechnologies.com/Chemi ... ntentID=36

Thanks for the pictures! That is the test I'm doing. After I add the solution to the pool water and mix, it stays completely clear and never gets cloudy.

When I get home from work I'll do a full set of tests to post up here.

 

[JohnT]

Take a sample of your tap water in and have them test it for you. See what CYA number they get from that.

I'll do that, I'm guessing CYA in tap water is 0 so it will tell me if their machine is reading it wrong?

Yep.

 

[brianmcb]

you guys were right, i took another sample (and a bottle of tap water) to the store and told the guy about the discrepancy. he did a manual test and another computer test and both came back 0.

 

[Butterfly]

you guys were right, i took another sample (and a bottle of tap water) to the store and told the guy about the discrepancy. he did a manual test and another computer test and both came back 0.

Yep! Now you have the TF-100 test kit and resources from TFP. You should trust your own testing

Where are those #'s you were gonna give us?

 

[brianmcb]

sorry i won't have them till tonight

my water cleared up quite a bit yesterday and i could finally see the bottom of the deep end. i noticed there was way more junk on the bottom than i thought. i picked up a leaf rake attachment and spent 1-2 hours pulling out leaves, dead mice, and other stuff from the bottom. there was so much down there, i filled my wheelbarrow with all the stuff i pulled out. after stirring it all up the water was very cloudy again. i figured there was no point in testing with those conditions, plus we are getting 2+ inches of rain. i did test FC and it was 0 so i shocked (with bleach) before going to bed.

this morning the water was VERY clear and blue. filter pressure had risen 8 psi overnight so i backwashed and added more DE before going to work. FC was back to 0.

unfortunately i didn't have enough bleach to shock again but i will this evening. i'm hoping my frequent backwashing is coming to an end, there is very little debris left in the pool and the water is quite clear. i took pictures when it was still a swamp so it's going to be fun to compare the before & after :-D

 

[brianmcb]

just for kicks here are the numbers from the pool store (from last night, before i cleaned out the leaves and stuff). I verified the pH reading by testing it myself (it was 8.0 before, I was trying to drop it to 7.4 but overshot it).

pH - 7.2
TA - 62
FC - 0
TC - 7.5
CH - 140
CYA - 0

tonight i will get a full set of results with my test kit

 

[frustratedpoolmom]

So when are you planning to add CYA

 

[brianmcb]

So when are you planning to add CYA

hah, tonight maybe? i'll pick some up when i get bleach. also, i'm not positive on the volume of my pool since it's free form. is CYA a good chemical to use to derive it? by adding x ounces, and CYA goes up y, i can derive the volume using the pool calculator? can someone post the equation if they have it?

i thought i should wait until i was pretty much done backwashing before trying to balance anything, was that a bad idea? luckily it's been really cloudy and rainy since i started adding bleach.

 

[frustratedpoolmom]

You can add the CYA via the sock method - tie it in front of a return that way you can still backwash.

To determine Gallonage, why not try it with Baking Soda instead...it and PH are a tad low, according to those last results.
Do you have a rough estimate, or is 20,000 it?

 

[brianmcb]

You can add the CYA via the sock method - tie it in front of a return that way you can still backwash.

To determine Gallonage, why not try it with Baking Soda instead...it and PH are a tad low, according to those last results.
Do you have a rough estimate, or is 20,000 it?

20,000 is my rough estimate, but a couple pool companies agreed that the number should be close.

What should my TA be? According to pool-school/water_balance_saltwater_generator I am in the range, although barely. Should I aim for the middle of the range, 75?

To go from 62->75 TA, using volume of 20k gallons, the PC says I should add 61 oz of baking soda. Playing with the numbers a bit...
if my pool is actually 15k gallons then 61 oz of baking soda would raise TA to 80
if my pool is actually 25k gallons then 61 oz of baking soda would raise TA to 73

so this seems like it would be pretty safe and allow me to figure out my pool volume. in both cases it says the effect on pH will be very minimal (raise it by just a few hundredths)

do i just add the baking soda at one of the returns? how long do i have to wait before testing for the new TA level?

 

[Richard320]

i took pictures when it was still a swamp so it's going to be fun to compare the before & after :-D

Well, share them!!

 

[duraleigh]

Brian,

The most accurate TA test (drops based) is plus or minus 10ppm. YOur pool store result is no better than that. I would suggest you leave TA right where it is and don't bother with it unless you experience some pH issues.

 

[brianmcb]

Ok sounds good, I'll leave TA for now.

Question about adding CYA: for 20k gallons I'll have to add a lot, around 200 oz. That's a huge sock! Should I add just a bit at a time? Use multiple socks? I bought stabilizer at Lowes.

I'm still not home, I'll post the pics and test results later.

 

[duraleigh]

If your water is clear and you forsee no reason to backwash, I would simply pour it slowly into the skimmer and let the pump take it into your filter where it will dissolve over the next few days (perhaps as long as a week).....just don't backwash during that time or you will wash out the undissolved CYA.

 

[frustratedpoolmom]

Since you are still trying to clear a green swamp, use the sock method, if you have multiple returns you can do more than one sock at a time, 2 lbs or so at a time... you can also set a sock off to the side in the skimmer so it doesn't block the flow of water. This way you can still backwash.

 

[brianmcb]

Actually I think my backwashing is coming to an end. 18 hours since the last time
and pressure has not risen. The water is getting quite clear and blue. I'll post photos when I get home.