Oops, FC, how high is too high?

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C

CountryBoy19

0
Mar 22, 2017
49
Bedford, IN
Pool Size
13000
Surface
Fiberglass
Chlorine
Liquid Chlorine
Long story short I lost my patience trying to get chemistry balanced after opening my pool for the season. For 2 weeks, every night I was losing 20+ FC in an overnight loss test. No idea what I was fighting but it got the best of me and in a bout of frustration I dumped 3 gallons of 12% in. And now I have FC of 59...Will it hurt anything? Bleach swimwear? Burn eyes? Should I just wait it out?

CYA: 65
TA: 100
FC: 59
CC: 0
 
CountryBoy19 said:
Long story short I lost my patience trying to get chemistry balanced after opening my pool for the season. For 2 weeks, every night I was losing 20+ FC in an overnight loss test. No idea what I was fighting but it got the best of me and in a bout of frustration I dumped 3 gallons of 12% in. And now I have FC of 59...Will it hurt anything? Bleach swimwear? Burn eyes? Should I just wait it out?

CYA: 65
TA: 100
FC: 59
CC: 0
Click to expand...
So you counted 118 drops to get a FC of 59?
 
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mustard algae slam level is 40.5 fc for your cya of 70.
Its ok to maintain that for 24 hours.
Above that ppm you are risking all that you mentioned including possibly damaging your surfaces/equipment.
It is safe for swimmers up to normal slam fc level for your cya (28ppm fc for you).
Your addition should have added 29ppm fc.
It should burn off but no swimming until fc is normal slam level or below.
If it doesn’t come down to MA range soon you can use peroxide to lower it.

When you say you were losing 20ppm fc nightly - were you testing after your addition to confirm you actually reached your target? That’s a large loss
 
JoyfulNoise said:
The quick and dirty rule of thumb is this - the amount in oz of 6% bleach it takes to raise your FC by X ppm's is equal to the amount of 3% H2O2 needed to lower the FC by X ppm's. That rule of thumb is good to use because it's a lot easier to find 3% peroxide in a drug store and most people use peroxide as an FC lowering chemical in spas where the water volumes are A LOT lower.
Click to expand...
 
Mdragger88 said:
Your addition should have added 29ppm fc.
It should burn off but no swimming until fc is normal slam level or below.
If it doesn’t come down to MA range soon you can use peroxide to lower it.

When you say you were losing 20ppm fc nightly - were you testing after your addition to confirm you actually reached your target? That’s a large loss
Click to expand...
Hmmm, you're right...there's a chance I miscounted jugs but not miscounted by 3...I'm not exactly sure how it got that high, I was testing the water daily.

I was not testing after each addition though.

That being said, what type of damage to surfaces? It's a white fiberglass pool that is 30 years old and already needs a total resurface job. Am I risking structural integrity of the pool or plumbing? Or just surface color (bleaching)? There's nothing fancy about my old pool so bleaching of surfaces isn't a concern of mine.
 
CountryBoy19 said:
Hmmm, you're right...there's a chance I miscounted jugs but not miscounted by 3...I'm not exactly sure how it got that high, I was testing the water daily.

I was not testing after each addition though.
Click to expand...
It is possible that you were previously using degraded (old) chlorine & not actually reaching your target so it appeared in the AM that you had massive fc loss, When in reality your bleach just wasn’t as potent as you thought.

Do a true Overnight Chlorine Loss Test once fc level drops to slam after the pool is clear.
CountryBoy19 said:
That being said, what type of damage to surfaces? It's a white fiberglass pool that is 30 years old and already needs a total resurface job. Am I risking structural integrity of the pool or plumbing? Or just surface color (bleaching)? There's nothing fancy about my old pool so bleaching of surfaces isn't a concern of mine.
Click to expand...
If it’s already white & worn this one time infraction will probably be ok. The surface/finish is the main issue usually with fiberglass. Obviously you don’t want to make a habit of this type of thing.

The higher the fc the faster it falls/burns off so hopefully by tomorrow with sun exposure it will have fallen to more reasonable levels. If not, you can go the peroxide route to help a bit.
 
Mdragger88 said:
I am curious what your cya was at closing
& also if it was 70 upon opening.
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I make sure it's 50 at closing. It was below 10 when opening. Winter CYA loss has been a problem in my pool but I can't explain why it disappears. For more info see this thread in the deep end where I responded with a lot more detail.https://www.troublefreepool.com/threads/degradation-of-cyanuric-acid-cya.292461/

Mdragger88 said:
It is possible that you were previously using degraded (old) chlorine & not actually reaching your target so it appeared in the AM that you had massive fc loss, When in reality your bleach just wasn’t as potent as you thought.
Click to expand...
I think that was definitely a factor initially. The very first bleach I used was leftover from the last season but I switched to new, fresh (production dates within 1 month) bleach a full week before I added the 3 or 4 gallons out of frustration. I did switch manufacturer/source for the bleach the day before the incident so I've questioned if maybe the advertised strength was off on the later bleach.
 
For future reference- when the
SLAM Process is needed don’t increase cya past 30/40 as it takes more liquid chlorine to complete the slam at higher fc levels. Best to wait until its over. Did you overshoot your cya target?
 

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Mdragger88 said:
For future reference- when the
SLAM Process is needed don’t increase cya past 30/40 as it takes more liquid chlorine to complete the slam at higher fc levels. Best to wait until its over. Did you overshoot your cya target?
Click to expand...
Yes, accidentally overshot target. I started from 0 when opening the pool for the summer, CYA was coming up slowly, was up close to 30 IIRC, added more trying to hit 40-50. Then my next test I got a reading that seemed to go back down (around 10 or so). Rather than slow down and retest when I got the confusing reading, I plugged it into poolmath and added the recommended amount. The next test CYA was way too high. I realized after the fact, that my test before the last CYA addition must have been messed up. I'm not sure what I did but I ended up with high CYA. This spring was by far my most frustrating at getting my pool chemicals balanced. Likely partially my fault, I've been so busy at work and home and wasn't giving it my full attention.
 
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Oh well, It happens! Just follow the chart & will work out! The smaller the pool the easier it is to overshoot things.
Good news is that you know what to do & how to correct based on your testing.
How’d it turn out?
Did you complete the
SLAM Process passing all 3 criteria?
 
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