CYA-Chlorine chart and Pool Calc differ big-time?

[gsxrken]

at least for the Shock value where CYA = 80.

Pool calc is saying 21 is my shock goal, but the CYA-Chlorine chart on this site says 31 or (30 for SWG like me).

Is this is known difference, am I mis-reading something, or (in either case) any suggestions as to which to use?

My pool is clear with only .5 CC but my FC keeps slipping even with 80 CYA and SWG set on 80% running 12 hours a day. I've decided to shock it to see if I can get to a state where the SWG can maintain the 4-6 FC I want to see.

 

[Butterfly]

Yes, the CYA/Chlorine chart is a little more aggressive than the PoolCalculator for shock levels.

You can shock anywhere in between the two and be in range for shocking, but I normally recommend the higher shock level.

 

[dmanb2b]

GSX, before shocking, try performing the overnight FC loss test. If you pass there is no need to shock. If I recall correctly you have really high CH and rising PH. I know this is a new pool, but that combo could lead to SWG cell scaling. If you can pass the OFCLT, I would first inspect the cell to make sure the plates are clean and also confirm your salt level is adequate

 

[gsxrken]

Interesting. Do you think enough scaling could occur in 2 months if as has been the case my pH keeps swinging into the 8s?

 

[JasonLion]

There could have been significant scaling, especially with your PH getting too high, though it really depends on your other levels.

 

[dmanb2b]

Yup...especially if CH is above 400 and you allow PH to rise above 7.8.

I live in Dutchess cty and deal with high CH fill water by taking advantage of rainfall (I backwash and lower the pool level before I know we have a nice t-storm coming ) and keep TA at 60 with PH never above 7.6. SWG has been clean for 2 straight seasons.

 

[gsxrken]

Ok- well, I just inspected the cell and it is spotless. Good news there. I will do an overnight loss tonight/tomorrow. I am prepared for a shock with 12 182 oz bottles of bleach, and suspect I will need them.I was down to 1 FC when I checked. Will update manana.

 

[dmanb2b]

Good luck....raise FC back up to the 6-8 range and re-confirm FC tonight, before performing the OFCLT