cyanuric acid - partial drain & refill questions

[chitown]

i have read that cyanuric acid is heavier than water so when you do a partial drain and refill to lower the levels you should:
1. turn off pump for a couple days
2. cyanuric acid will settle to bottom
3. partial drain from bottom of pool
4. refill

i have also read that you should drain from the top. this does not makes sense since the acid should be heavier, but it was recommended at a pool stores website.

questions:
which method is correct?
does it really matter?
do i really need to have my pump off for a couple days?

thanks!

 

[JasonLion]

Welcome to TFP!

CYA is uniformly distributed throughout the pool. The concept that CYA "sinks", or "floats" for that matter, is a myth, and has no basis in reality at all.

It doesn't matter where you drain from, and there is no reason to wait at all.

 

[Guest]

CYA is dissolved in the water much like salt or sugar is dissolved in water. What you are suggesting makes as much sense as trying to make a cup of coffee less sweet by only removing sweetened coffee from the top or the bottom of the cup. The only way to reduces the sweetness is to pour out some sweetened coffee and replace it with unsweetened coffee It matters not where in the cup the sweetened coffee came from.
Likewise with CYA!

Unfortunately, there are a lot of myths and misinformation in the pool/spa industry that is accepted as the truth, often because someone with no real understanding of pool chemistry is misinterpreting something they read or hear. This is pretty much how the fallicy of 'slugging' acid in a still pool to lower TA got started.

Getting back to CYA, if you think about it does it really make any sense that something dissolved in water is going to be hanging out at the top (or bottom or by the tiki bar, for that matter ) or is it going to be equally distributed throughout? Just because the water is in a swimming pool it doesn't mean that the laws of chemistry and physics are thrown out the window!

 

[chitown]

fair enough. i will wait no more! drain and refill (from where ever my pump lands).

 

[perry32]

old thread but simple follow up question: does this hold true for calcium hardness as well?

 

[AUSpool]

Exactly the same, it will dissolve and mix uniformly. Like a teaspoon of salt in a bathtub of water. Which applies to all the main parameters, FC, TA, CH, CYA, borate and the acid for pH management. The mith may have originated from stratification which is mostly a function of temperature.