No Free Chlorine, Swg, Cya Over 140

[madorh]

I have new plaster pool (last fall), SWG never used then before close but was started up in May. 28,000 gal, DE filter, running 12 hrs/day. Was crystal clear at opening(and still is). initial store test showed: CYA 93, TC and FC 0, pH7,alkalinity 152 and total hardness 222. Shocking commenced...problem is can't maintain free chlorine. I have visited the pool store for testing roughly every 2-3 days, kept my ph and alkalinity ok, but now CYA is 151 after dumping all told 25 lbs. of stabilized shock (on pool stores recommendation... I was unsure if the SWG was working and Jandy was out yesterday - could not find a problem but replaced the cell anyway with new one. Even with SWG off, we dump 3-5 lbs. of shock in, FC is 5_10 on my strip or so, in 24 hrs. is down to 1.0 and in another 24 hrs. is 0.Store said to check phosphates - initially >500 and phosfree used. 2 days later was 100 in store, but Jandy's guy measured >1000 1day later! ?? AND FC 1agin after 24 hrs. of shocking.I have spent over $250 on shock and other chemicals. I drained the pool about 2 inches down but don't thinkg this will help CYA much(at least not according to your chart). I don't know if I need more phos free or not. Still can't maintain free chlorine, CYA level very high but have read different things on that and unsure if I should drain some more out. SHould I do bucket test now? Do I need to worry about CYA being so high? THe store has never even mentioned it as a problem - only found out by internet myself. I know now to use bleach instead of stabilized shock they sold me (25 lbs. of). SWG now at 100% since new cell put in last night and FC about 1 on strip this am. WHat would you suggest? I am getting test kit today too....

[PaulR]

CYA (stabilizer) acts to protect chlorine from sunlight by binding some of the chlorine to the CYA molecule, and leaving the rest of it as the active sanitizer. As the active sanitizer is used up, some chlorine is released from the CYA (it's an equilibrium). The more CYA you have, the more chlorine is bound to it, and the less active sanitizer you have (for the same apparent FC level). This means the same FC level becomes progressively less able to keep the pool clean, as CYA goes up.

I'd say your pool is overstabilized and you have an algae outbreak that the active sanitizer is unable to keep up with. You need to drain the pool about halfway, to lower CYA by half (i.e. to about 75) which is a good level when you're using a SWG. When the CYA is lowered, then it becomes more practical to shock the pool with liquid chlorine/bleach to defeat the algae.

--paulr

[polyvue]

Yes, 1 PPM Free Chlorine is not even close to being a maintenance level when you have a CYA of ~150 PPM. See Best Guess CYA chart

So, after you've followed PaulR's good advice on draining half of the water to reduce CYA and then refilled, ramp up the chlorine - using 6% bleach or 10-12% liquid chlorine - as per the Best Guess chart (linked above) to shock the pool until there is less than a 1 ppm drop in Free Chlorine (FC) from dusk to dawn. At that point, set your SWG to ensure that the minimum chlorine level is held. Target a Free Chlorine level of 5% or more of CYA. (If your CYA = 75 ppm, you may want to aim for 4 PPM FC)

Lastly, don't worry about phospates. Pools have varying amounts; keep your chlorine level good and algae won't have any opportunity to take advantage of them.