New pool, CYA=0 intentionally, what should be the FC shock level?

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lennyf

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Dec 8, 2013
14
I just started a new 25K tiled pool. The pool has some kind of enclosure so it is pretty much protected from direct sunlight during the day. It has been open already a week, with FC around 1 and pH around 7.8, with only bleach added (no other chemical whatsoever). Water were sparkling clear. Now for the tricky part: yesterday evening FC was less than 1 so I decided to have little leeway and bump it up above 2. I added 2.4 ppm. Water are still good. After letting the pump run for an hour I also added about a quart HCL to lower pH to 7.6. The pump still running. A couple of hours later I went out to check on the pool. I almost blacked out. The pool was completely cloudy, with dense white powder throughout the water! I didn't know what it was, and I certainly did not suspect algae breakout. Instinctively I related this to my last action (pouring the acid). I forgot to mention TA and CH around 250 both. But if at all, acid dissolves this stuff and not precipitates it. So I was clueless. Decided to go to sleep and re-check in the morning. morning came, test results (k2006):

FC = 2.5
CC < 0.5
pH = 7.6
TA = 300
CH = 200

It didn't loose even 1 ppm overnight!
Now the water condition: most of the powdery white stuff sank to the bottom, I'd say something like 10% still remain suspended. Now it's evening, filter pump has been on all day. Filter is not clogged yet (return jets are still strong), and I think I noticed just a little tiny weak greenish taint on the white grout lines at the bottom of the deep end. Current conclusion: May be I succeeded to catch the algae in the beginning. So Why am I addressing this highly respected forum members? Here are my questions:

0. Could it be something not algae?
1. According to the CYA/FC tables I was well above the min FC for zero CYA. So why is the outbreak?
2. If somehow the table is wrong, what should be my current shock level? and my normal level?
3. Will the remaining white powder go away by itself? (of course pump running)
4. Is brushing the floor absolutely needed?
5. Is it safe to swim? Or at least only for me to enter for floor brushing?

Big Thanks to all replies, remarks and advice!
 
0) Indeed, not algae. From your test results it is almost certainly calcium clouding.
2) With CYA really at zero, normal FC is between 1 and 2, shock level 5.
3) Lower the PH to 7.2, and longer term lower the TA.
4) You need to brush at least weekly, no necessarily right now. Right now I recommend vacuuming up as much as you can.
5) FC is a little higher than I would recommend for swimming, though nothing too dramatic will happen if you do.

Your TA is very high, coupled with a normal CH level you are very much at risk for calcium clouding. The only sure way to get rid of calcium clouding is to lower CSI below zero, which in this case means lowering TA.

I very much recommend using at least a little CYA. CYA around 20 will make things much more stable and reduce the amount of dangerous forms of CC that might accumulate. Adding some CYA will also allow swim suits to last longer.
 
Thanks JasonLion,
Is calcium clouding common? Could it be that adding the acid for the first time triggered it? Could adding additional acid (while lowering the pH) also dissolve the clouding?
Is it safe to swim in the remaining calcium cloud (regardless of FC)?
 
If is not safe to swim unless you can clearly see the bottom of the pool.

Calcium clouding is common when TA and CH are both high, rare otherwise. It would not have been brought on by acid, most likely it was adding chlorine that triggered it.

You don't want to lower PH below 7.0. If you could that would speed up clearing the water, but it would also risk damaging the pool.
 
There are reasons to use CYA even in indoor pools as it provides a buffer for FC as well as sun protection, in general we suggest a CYA level of 20-30 ppm even for indoor residential pools.

Ike
 
I don't understand why there is a need for minimum amount of CYA even if the pool holds very well its FC. I waited three days before re-posting so I could check it carefully. In 3 days and nights, without swimmers, FC went down hardly 0.5 ppm! CYA buffers the chlorine so it is more stable but at the price of less oxidation strength. Therefore you need more of it. So if my FC lost is minimal without it, why use it? Are there really specific types of organic matter that chlorine w/o CYA cannot handle (like JasonLion hinted)?
 
You misunderstood what I was saying.

Chlorine breaks down organic matter in several steps. Some of the intermediate breakdown products are potentially harmful. Having CYA in the water, even at fairly low levels, greatly reduces the creation of some of the more dangerous breakdown products, favoring instead some of the less harmful breakdown products. Without any CYA, typical chlorine levels are also very harsh on bathing suits. Having a little CYA in the water can greatly increase the lifetime of your bathing suits.
 
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