Shocking question(s)

[tcat]

(not that shocking). My FC had been losing more than expected lately (after lots of rain, a 30% refill, lots of pollen, and 1st use). Kept bringing it to 5.0 and next morning it's 1-2. CYA 45-50, TA 75, CH 340, pH 7.6. Clear water, no visible signs of algae.

Decided to shock this morning since I hadn't shocked for at least 6 months. I had some "Zappit" from the previous non-BBB owner, so I threw 4 cups in, only got it up to 10. Decided I'd use Clorox for the rest of it, 1 gallon got it 16.5, just what I was looking for.

My questions:
Can I check CYA while at high FC? (I was just wondering how much the Zappit might have raised it, since that might effect shock level needed).
Can I check CH while at high FC? (Zappit is supposed to raise it, just wondering how much).
How many hours does the FC need to stay at 16.5? Just the overnight not more than "1" drop?

 

[jblizzle]

Zappit is cal-hypo. It will raise the CH not the CYA. You can test CYA anytime you want, wait an hour after adding zappit to test the CH.

You maintain the shock FC level until you pass the 3 tests to stop:
pool-school/shocking_your_pool

 

[tcat]

Thanks. I already had CC below .5, so really the overnight one is the main one I need to pass. So I keep it at 16+ until it gets dark out, right?

Checked my CH and it's 300, down from 340. I must have got the 340 before I did the 30% refill

 

[jblizzle]

Yes. Test after the sun goes down and again before it comes up.

 

[tcat]

Looking good. FC went from 16.5 to 15.5 from 3:00 PM to 7:00 PM. I bumped it to 17.5 at 7:00 PM (checked at 8:00). Was 17.0 at 7:00 AM, CC less than .5 (although did turn faint pink, so has maybe .25).

Off to buy some fiberclear and do a clean backwash this weekend. Ran out of DE, figured a great time to try something new.

 

[duraleigh]

figured a great time to try something new.

Maybe, maybe not. If DE has been working for you, I suggest not changing.

Fiberclear hasn't been around long enough to really prove itself and, if you search the forum, I think there may have been some issues posted by other members.

 

[tcat]

Maybe no so good.... it's not right for FC to go from 17 to 11 in the next 12 hours is it? Actually a cloudy cool day today. CC is still under .5.

Also I read enough positive threads about Fiberclear and Zeofiber, I picked up some Zeofiber to try out. Can always go back.

 

[jblizzle]

Yeah that is probably OK. You lost 35% of your FC which seems reasonable for a CYA of around 50 ppm.

Once down at normal levels, say 6 ppm, if you lost 1/3 a day that would only drop you to 4 ppm ... which at 2 ppm lost per day is totally normal.

 

[tcat]

Thanks! I was worried. Good news about Zeofiber. Just added 12 cups (recommended for 48' DE), and my pressure went from 16 psi (no media) to 18 psi, it always started at 20 with DE. Will wait a couple days to see how the water looks. It is more expensive than DE, but a 3# bag was $13, and it will make approx. (2-3) 12 cup cycles. Very light, very eco friendly.

edit: 24 hours later pool is clearer than ever. With pool light on I see no particles at all. Filter is at about 18.5 psi (it was never below 20 with DE). I probably should have taken filter apart and cleaned it with a hose on the changeover, plan to next time I need to backwash, I was just anxious to try this stuff. I did backwash 5 times with rinse between each, so should have cleaned fairly well.

 

[tcat]

Well, everything was going well until tonight. Not adding any Clorox after shocking:

FC = 17.5 7:00 PM CC = <.5
FC = 17.0 7:00 AM CC = <.5
FC = 11.0 7:00 PM CC = <.5
FC = 10.5 7:00 AM CC = <.5
FC = 6.0 6:00 PM CC = < 1.0 <<< CC went up

Water crystal clear entire shock process. Why would the CC all of a sudden go up?

Yeah that is probably OK. You lost 35% of your FC which seems reasonable for a CYA of around 50 ppm.

Once down at normal levels, say 6 ppm, if you lost 1/3 a day that would only drop you to 4 ppm ... which at 2 ppm lost per day is totally normal.

 

[linen]

Did you happen to get rain, swimmers, or other organic debris in the pool today? If yes, check it in the morning and see if the CC is still there.

 

[tcat]

No swimming or rain. I did backwash about 6" out and refilled, and switched DE to Zeofiber. I'll check in the AM.

 

[davelinde]

Yeah that is probably OK. You lost 35% of your FC which seems reasonable for a CYA of...

I am in the middle of my first ever shock and learning. This matches what my wife told me, but I don't think I've read anywhere yet? So in the absence of organics reacting with FC to consume it... in any 24 hour period with sun etc it will drop in proportion to the total amount but moderated by the amount of stabilizer? It makes sense, but I was not sure how it worked.

All I know for sure is that we had measurable CC and now we don't, but we are still losing FC at some rate. For whatever reason (don't ask) I don't think we've managed to actually test a loss over night yet - we have a few measures of loss but they all include some random amount of daylight hours.

 

[jblizzle]

tcat:
Do you have city water? Some cities are using CC for sanitation. So adding a bunch of water could be where the CC came from. Test your tap water and see what you find.

David:
Only 2 things consume the FC: organics and the sun. So even if you have no organics, the sun will cause a FC loss (thus the OCLT to isolate organics). The % thing I think is roughly true. It gives a sense of what to expect, it may not really be a constant % as FC level changes for a fixed CYA.

 

[tcat]

Tested this AM, bingo! CC back below .5. Odd my FC actually went up to 7.5 (from 6). Didn't have my filter running, sample about 15" deep, maybe just a "hotspot". Will test again tonight with filter running for an hour or so. Will be time to start adding Clorox again.... and test my DIY chlorinater! So you can really only go 3 days without adding chlorine after shocking... not good enough for a 1 week vacation. Hopefully my feeder will work, if not back to pucks for a week. I actually like CYA a little above the "norm" of 50, I was using much less chlorine with it at 70-80.

 

[linen]

Letting your cya go up is okay, but you will then need to be vigilant in keeping your FC above the minimum for that cya level as to prevent algae...cause once you get it at high cya levels you got a fight on your hands.

 

[davelinde]

The % thing I think is roughly true. It gives a sense of what to expect

The % thing matches with my observations - eg, when the FC levels are higher the absolute value drops by more each day than when the values are lower again. Nice to know this matches the science. For some reason I was thinking the losses were due to a fixed rate kind of thing so FC drop would be linear, clearly it's not.

THANKS!

 

[tcat]

Shock Summary:

FC = 17.5 7:00 PM CC = <.5
FC = 17.0 7:00 AM CC = <.5
FC = 11.0 7:00 PM CC = <.5
FC = 10.5 7:00 AM CC = <.5
FC = 6.0 6:00 PM CC = < 1.0 <<< CC went up
FC = 7.5 7:00 AM CC = <.5
FC = 6.0 7:00 PM CC = <.5

Very happy. Will start adding Clorox tomorrow. I must say my switch from DE to Zeofiber a couple days ago has my water looking drinkable. With DE I always saw "particles" in it. Filter pressure is also staying at 18-19, lowest it's ever been!