Will liquid chlorine sitting in a storage tank that is 12.5 % strength weaken/degrade at a faster rate than 12.5% diluted to 6 or 8%?
12% loses strength way faster than 6% or 8%. However, dilution is not always a good idea. Dilution can speed up the breakdown, depending on what impurities are in the water.
Possibly quite a bit, though the exact amount very much depends on temperature. There is a chart towards the bottom of this page that can give you a general idea.
The more you dilute the chlorine, the faster you will need to inject it into the pool to maintain the same FC level and the sooner you will need to refill the tank. How big is the tank and how much chlorine do you use in a week?
But will my 12.5% still be at 12.5% say after 30,40 days just sitting in that storage tankSo assuming 2 quarts per day and if the chlorine is 12.5% initially then you will only get 50 days out of 25 gallons of full strength. When you dilute the chlorine, you will shorten the time between refills. So at 6% chlorine, that is 24 days between refills. 3%, 12 days, etc.
I would be satisfied with refilling every 2 weeks .. I'm understand that using a diluted chlorine results in using more volume to get the same amount of chlorine (2qts of 6% hypo = 1 qt of 12%)No, you would still need to take that into account. I was just trying to demonstrate that the more you dilute the chlorine, the faster it will be used up. There is a sweet spot where you would probably get the longest time between the refills which balances degradation with injection rate but is going to be a complicated calculation because the concentration changes over time and so the injection rate would need to change as well. So it is probably best to dilute as much as possible so you are dealing with a near constant concentration but it means refilling more often. I would first target a 3% concentration and see how that goes. That should last almost two weeks.