TA - CYAf

[markmac]

I've been trying to maintain my new pool for a couple months now, and after a battle with super high CYA (well in excess of 100), I did a 3/4 drain and its now down to 50-60ppm.

Since the drain, I've been only using clorox and Muriatic acid. From my past month of experience since the drain, I'm averaging a chlorine burn of at least 5ppm/day, and need to add 4-6 cups of acid every 3 days to keep the PH down.

It seems like my PH is constantly rising, and from what I can tell from reading the forms, I'm burning Chlorine fairly fast.

I have the K-2006 test kit, and in the book it states I need to consider this Cyanuric Acid correction to my TA. When reading up on TA, it states that if my TA is not in the ideal range, my PH can bounce quickly, which is what I am seeing.

Here are the readings straight from the tests;

FC - 10
CC - 0
PH - 7.8-8.0
TA - 90
CH - 320
CYA - 55

If I use the Correction table, my CYAf is 0.35. So using their formula [90-(55X0.35)], my TA would be 71 (90-19).

Given I'm new to all this, I wanted to confirm I'm understanding this correctly? Also, what would be my first course of action? Do I increase my TA with baking soda? If so, how long do I wait before re-testing and then work on PH?

Would this be the cause of why I am burning through FC so fast?

Thanks

 

[Butterfly]

FC - 10
CC - 0
PH - 7.8-8.0
TA - 90
CH - 320
CYA - 55

Your numbers look fine.

To help with the pH rise, I suggest you lower your TA, not raise it. Each time your pH reaches 7.8, lower it back to 7.2 with muriatic acid.
Over time it will drop. Keep a log of how the pH is doing and when it reaches its happy spot, time to leave the TA alone.
Let us know if you end up heading for TA of 50ish.

The most common reason for pH rise is aeration. It could be people in the pool splashing, kids playing, waterfalls, anything that makes some bubbles. Got any of that?

Your FC use could be normal or not. What is the average daily use of your pool? # bathers? kids? full sun? water temp high? lots of variables to add to the mix.

You can do an OCLT to rule out organics.

ETA: Great job on lowering the CYA

 

[JohnT]

Raising your TA would cause your pH to rise faster. If your plaster finish is new, or you have a waterfall or other feature that results in a lot of splashing, you may have to just accept pH rise. It should slow down over time as the plaster cures.

I can't really comment on what kind of usage you'd see where you are located, but if you have any doubts, it might be worth performing an overnight chlorine loss test. Measure your chlorine, preferably with a FAS-DPD test after dark in the evening, and then before daylight in the morning. You should see less than 1ppm loss. You are checking for a biological chlorine demand. If you have an overnight loss, you need to shock the pool. If you don't have an overnight loss, then that indicates that your chlorine consumption is primarily from the sun.

Is your CYA number from a pool store, or one you performed?

 

[markmac]

A few more details.

- The plaster is old, and in need of replacing.
- The pool is not really used much at this point. Maybe once every two days by myself who is not splashing or aerating it in any way..
- No waterfals, just two jets to circulate into the skimmer.
- Overnight chlorine test if good. No loss.
- CYA is my test. Prior to drain, the first few drops would hide the dot. Pool shop just stated >100.
- I've been dropping the PH to 7.2 every few days. But then its back to 7.8-8.0 after a 2-3 days.

 

[Butterfly]

Well, on the pH rise, I don't know. Do you have any air bubbles coming from the two jets?
Are the neighborhood kids getting into your pool when you are not home?

About the FC loss, older plaster would be more porous and rough and have more places for algae to sneak into
So, I suggest shocking the pool. It won't hurt and might be the answer! There could be a nascent algae bloom hiding in the old plaster eating chlorine.
See Pool School for directions on How To Shock Your Pool.

Brush daily during shocking, and make sure you brush the pool at least weekly for maintenance.

That is what I would do if it was my pool.

 

[JasonLion]

I have the K-2006 test kit, and in the book it states I need to consider this Cyanuric Acid correction to my TA.

All of our numbers/advice are based on using the TA number directly from the test. You should not do the CYA correction to TA unless you are trying to calculate LSI. We tend to use CSI instead of LSI, so we never use the CYA correction to TA.

Technically, TA is total alkalinity - the total resistance to PH going down. The CYA correction is a way to estimate carbonate alkalinity, the contribution to TA from carbonate in the water. Carbonate alkalinity is not a useful number by it's self, in fact we never use it. It's only value relating to swimming pools is because the formula for calculating LSI uses carbonate alkalinity as one of it's inputs.

In any case, there is no reason for your to raise TA unless you are using trichlor tablets.