CPO

Mind explaining that. pretty much everything that I've come across for breakpoint chlorination states something to the effect of:

Great info here. Thank you. So, here's my summary for the chlorine issue alone: Our CC was ridiculously high at 2-3 ppm. We needed to raise the FC level to 10x the CC level for shocking, which would bring the FC to 30 thus the calculation for so much Hypochlorite. The shocking worked (no CC measured) but the FC did not magically return to 3...and without outdoor factors (air exchange, sunlight, etc) the level would stay high without chemical intervention. In the future, we should either replace water regularly to keep CC, CH, & TDS all low and/or shock when CC first becomes measurable (.5 ppm) This shock would only be enough to raise FC 5ppm and would be more easily lowered (naturally or chemically). Does that sum it up well enough?

Added a bit more Sodium Thiosulfate and tested again: Free Chlorine 3 Total Chlorine 3 Yay! No chloramines. pH 7.0 We adjusted pH down while chlorine was high. Now we've removed the chlorine and the pH went back down, of course. A bit of soda ash & we're good to go.

I wasn't sure about remaining chlorates(ites?) after treatment. If there were no issues, I would expect this to be an approved use/marketed for this use with calculations to lower by ppm/gal. I couldn't find a reliable reference off hand, but was considering due to cost. We've used 19lbs of sodium thiosulfate so far...still reading ~10ppm, though it's decreased substantially. Current tests: CYA 0 -- We don't use for an indoor pool Free Chlorine 10 PH 7.2 Alkalinity 65 Hardness 500 -- Yep...really need to change the water

I'll not defend the choice not to change the water...that's obviously been a chronic issue. I'm new on the scene here and need to get this taken care of quickly. Currently my only options are: Add ~18lbs of Sodium Thiosulfate Add Hydrogen Peroxide??? How much, health issues? Drain (X)% & refill.

Sorry if I sound like a noob on shocking...but I am. This pool hasn't been shocked or had it's water replaced for 12 years. So...too much cal-hypo & reccommend bleach instead. ...what would be recommended for a 2ppm CC? After shocking, how do we return to safe, swimmable levels? The chem out probably worked & lowered it 5ppm (with 4 lbs), but it didn't lower it to measurable levels. Do I need to add 20 lbs or so of chem out? That's $200... I assume this isn't standard after shocking...how do we raise the chlorine level to shock and get them to drop afterwards? Or do we just not shock?

The pool where I work is a 100,000 gallon indoor tile pool heated to 82'F with a 240sq ft DE filter & flows 240gpm. We use only granulated Calcium Hypo to sanitize. The pool has been crystal clear, but did have some mismanagement problems...old water & lack of shocking. For the first time ever we decided to shock the pool. The FC level was 3ppm and the TC was 5ppm. We calculated 35lbs of Calcium Hypo shock the pool. The amount of stuff that precipitated out of the water was huge. The DE filters clogged up overnight (we dumped & washed them and put them again), and we vacuumed the floor deckside with a 100 sq ft unit and clogged it in 30 minutes. The water is clear again and there is nothing on the bottom of the pool. Chemical readings show chlorine is off the chart (over 25ppm), even after dumping 2-2lb cans of Chem-Out! We can't even guess how high it still is. Two questions. Why is the level still so high? How do we get it down? Post-shock chem panel below. CYA 0 -- We don't use for an indoor pool Tot Chlorine >25 -- ! Free Chlorine >25 -- ! PH 7.6 -- Okay Alkalinity 42 -- I know...60lbs of Alkalinity Increaser to be added Hardness >400 -- Yep...need to change the water