1. ## Shock or not?

I have a SWG, pebble pool that looks great and the water is crystal clear, however..... when I test my FC & TC there is enough of a discrepancy towards the higher TC level that makes me think I should shock the pool according to my "The Pool Calculator". Basically it says that if my CC is above .5, which I believe it is, I should shock the pool based on the Pool Calculator recommendation of a shock level of 11. What I need to know is for how long? I just started adding CYA so my levels are relatively low (see below). Oh yeah, I just started using the BBB method with absolutely great results but I am still a newbie to this whole thing. I have had my pool for about three years and I have never shocked it. I have changed about 1/2 of the water once so far.

Mike

Pool Size: Apprx: 20,000G
FC= 2.0, TC = almost 3 which should translate to CC being higher than .5 (time to shock?)
pH= 7.6
TA= 80
CH= 280
CYA= 20
Salt= 3400
Temp= 76° (pool is in Mexico)

2. ## Re: Shock or not?

Hello Mike, Welcome to TFP

What kind of test kit are you using to determine FC, TC etc? In spite of the clear water if the CC is definitely above .5 ppm I would shock the pool. A constant 12 ppm FC level should work in view of such a low level of CYA. Shouldn't take long to get those combined chloramines down -- maybe just a day.

Here's an excerpt from Pool School that may prove informative:

Shocking:
• 1. Measure the FC level
2. Add enough chlorine to bring FC up to shock level
3. Repeat steps 1 and 2 as frequently as practical, as often as once per hour, and not less than twice a day, until:
[list:5npspmx5]a. CC is 0.5 or lower;
b. An overnight FC loss test shows a loss of 1.0 ppm or less;
c.And, if you don't have a FAS-DPD test kit, the water is clear
[/list:u:5npspmx5]

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