need help with the GREEN beast (have high CYA and TA)

[eli]

PHOENIX AZ. DARK green cloudy water for last 9 days - I am comfortable with TF-100 and pool calc usage but I am inexperience in execution.

date 9-14 6pm 96ish deg. ..................... date 9-18 12pm 98 deg.

FC 0 .................... FC 4.5
CC 0..................... CC .5
TC 0 ..................... TC 5
PH 6.8...................... PH DIDNT TEST
T/A 50...................... TA 110
CH 1000...................... CH DIDNT TEST
CYA 90...................... CYA 100

draining pool slowly replacing %10 at a time while back washing
I AM ABOUT TO ADD 5.8 GALLONS OF 13% LIQUID CHLORINE - how long do I have to keep FC at 39 to kill the beast?? is waiting till dark to add CHLOR worth it??
how is it the chlor level drops so quickly when my CYA is so high?

DISOLVED SOLIDS HIGH BASED ON PRIOR OWNER HAVING SWG

 

[JasonLion]

When you are just starting shocking you should add more chlorine as frequently as practical until the level doesn't go down as much (at which point you can slow down).

The total amount of time you need to remain at shock level is difficult to predict. It depends on how much algae you have, how diligent you are about keeping FC at shock level, and so on. A couple of days is fairly common.

 

[eli]

Thank you Jason,
I wizzed away 12 gallons of 13% chlorine by not keeping it at shock level, I have since read both long and short version of killing algae. I cannot afford to kill the bloom w/out replacing half the water to remove CYA, have a sump pump and this sunday off. Can anyone tell me risks associated with 50% water replacement to a 30+ yr old plaster pool with average high day temp being 87 degrees or night 64 degrees.

 

[Ohm_Boy]

I'm a little concerned with that ph of 6.8. Most testers bottom out at 6.8, and the ph might really be even lower. I'd feel better if it were 7.2 or so.

how is it the chlor level drops so quickly when my CYA is so high?

There are [primarily] two reasons for chlorine loss. 1) UV/Sun and 2) Organics in the water. CYA only helps prevent loss to UV, it cannot mitigate any loss to killing algae.
But you are correct in that high CYA will require you to use higher FC levels to fight algae, and you would be better served to reduce the CYA. I wouldn't foresee any significant problem with water replacement, but if you have concerns, you can do 1/4 or 1/3 at a time if you'd like, and simply do more than one replacement session until you hit your target CYA level.

 

[duraleigh]

eli,

I am with ohm_boy.......suggesting you get CYA lowered before continuing the shock process. Your current CYA level is so darn difficult to manage.......we see problem after problem when it's that high.

If your water is cheap enough and you are concerned about your plaster, you can simultaneously drain from the bottom of the deep end as you refill from the surface of the shallow end. You will use quite a bit more water but your water level will never leave any plaster exposed.

Another method that has been discussed (but to my knowledge, no one has ever attempted it), is to purchase a cheap plastic sheet that will cover your entire pool. Then start drawing off water from underneath the sheet as you refill water onto the top of the sheet. I suspect that may be manageable on a pretty small pool but not so much on a larger one.

One way or another, getting your CYA down to about 60 will really help you manage your pool. :lol:

 

[eli]

half of pool is drained, 20 gallons of sweet sweet 12.5% chlorine on hand. FC is at ZERO I am waiting for the water level to raise to skimmer level before adding chlor but might start sooner with sump pump circulating water. On second thought I will wait till after work tomorrow so I can keep my levels at sterilizing strength. PH is 8.2 which I assume will decrease with water replacement it would be good if it got to 6.8 before I start my shock. T/A is at 100 didnt run any other test as water is so concentrated now. Any thoughts?

 

[duraleigh]

Keep your pH in the 7's. 6.8 is as low as most tests go so you could be lower than 6.8 and not know it.

Once you add the chlorine, don't retest pH until your shock process is complete. The test will read falsely high.