Cyanuric Acid does go down right?

[PharmerAnthony]

Hi all, first post here, been browsing the site since I bought a home with a pool 2 years ago.

I have always had a pool service come put chemicals in my pool, at $50 a month I thought it was reasonable, but after an algae bloom this past Easter Sunday, I am going to let them go as this was the second time in a year this happened. Each time it did, I tested the water (with HTH strips) and sure enough the free chlorine (FC) was zero.

So now on to my question.

As of right now my CYA level is 30-50 (strips, yes I know, im ordering the TFT-100)
With lots of sun on the pool, How much will my CYA reduce weekly?
Why do I care? Because I would like to use trichlor tablets and trichlor shock.
Why would I do such a terrible thing? Long story short, I can get it at a very discounted rate, much cheaper than liquid Cl bleach.

My pool gets a lot of sun, full sun from 7am to around 4pm, then half sun from 4-7ish (730ish is around sunset right now).

I would like to use the tablets for convenience and cost, but would the amount added considerably outweigh the amount lost to UV penetration?

TIA

FWIW pool service used liquid chlorine and copper algaecide.

 

[RobbieH]

Nope, it does not go down unless you remove water, unless some really weird circumstances occur.

Am I reading your post right, you have an above ground plaster pool?

 

[PharmerAnthony]

That was a silly mistake, in ground pool! I fixed the sig.

For the CYA, I have read here and other places that sunlight breaks it down, why else would you have to add more eventually? Where I live, removing water is definitely not an option.

 

[mrcarcrazy]

Sun Doesn't break down CYA.

 

[RobbieH]

You would only add CYA due to:
LOTS of backflushing, which you won't do with a cart filter
LOTS of splash-out

That's about it.

If you can't remove water, you need to stay on a "liquid diet", or go to salt water chlorination. Tabs or granules are not going to be your friend.

 

[AprilNC]

CYA protects chlorine from being broken down by the sun ... but CYA is not broken down by the sun.

** Does not mean that chlorine is completely protected - chlorine still needs to be replenished

 

[PharmerAnthony]

****.

Thanks for the prompt replies. Ok, time to start shopping for NaClO

 

[AprilNC]

Add one of the recommended test kits to your shopping list - it will be key in determining what you need to add to your pool.

 

[jblizzle]

The other way to reduce the CYA (and CH) in the water is through hiring a RO service company, but only available in limited areas and generally cost more than just replacing water.

To be fair ... CYA does slowly get "consumed", but I think it is something like under 5ppm per month during the summer. In any case, exclusive use of tablets and granular chlorine is rarely going to be a good idea.

 

[SwimAustin]

I have 25 lbs of trichlor tablets, which are effectively free, because I already paid for them. However, it's still cheaper for me to use bleach, because I don't want to pay to replace water. I'll use them eventually, at least some of them.

 

[gwc]

Keep them for a time when you go on vacation and can't add chlorine manually. Regular sage will get your CYA so high that you will not be able to keep enough chlorine in the pool. The CYA/Chlorine chart http://www.troublefreepool.com/content/128-chlorine-cya-chart-slam-shock shows that as the CYA increases they amount of chlorine PPM needed to sanitize the pool increases. I had an Intex pool and it happened to me.