It should be brine, which shouldn't hurt. It can still be tested for potency. Somewhere around here I have have the "recipe". I think it's 10 ml added to 10 liters of un-chlorinated water (5 soda bottles) gives you the same dilution as adding 1 gallon of the stuff to 10,000 gallons of water. Then you can measure the FC level in the 10 liters and it will give you the concentration...3ppm means 3%.

Carl