Swg pool slight green cast


New member
Aug 11, 2014
St Louis mo
I need some help. We have a 4-year-old gunnite 20,000 gal swg pool. We opened it about a month ago and after brushing, vacuuming, and adjusting the chemistry, the water was fairlyclear and blue. The FC has been fluctuating from >1 ppm to <3ppm, and I have been adjusting the generator to try to come to some consistent FC level, hopefully around 3ppm. During this process the water seems to have acquired a very slight green cast. I’ve ordered a FAS-DPD kit to get some accurate numbers, but I’m still confused about how to use Pool Math to compute how much liquid pool shock I’ll need to have on hand. According to what I’ve read, I’ll probably need to bring the ppm number up to 31, but how much shock do I need to do that? Maybe I’m making it too complicated, but I don’t see the answer anywhere in the forum. I realize I need to have a starting number and a goal number (31).

Any suggestions on how to compute this are much appreciated.

FWIW, here are my current numbers:
FC 2
TA 80
PH 7.4
CH 124
CYA 80



Mod Squad
TFP Expert
May 3, 2014
Laughlin, NV
PoolMath does the calculations for you. Either the app or the webpage version linked at the bottom of this page.

While you are waiting on your kit to arrive add 5 ppm FC worth of liquid chlorine in the pool each evening. Are you running your SWCG? 1 gallon of 10% bleach will add 5 ppm FC to your pool.
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