My LHBS used to have a different Iodine sanitizer, can’t remember the brand, but now carries 5-star brand IO-star. The old brand had instructions for 12.5 ppm and 25 ppm Iodine solution. The new IO-star brand has instructions for 25 and 50ppm. I used to mix up the 12.5ppm solution for my kegs and never had a problem. So my question is what is the right mixture with the IO-star with out wasting excess sanitizer?
Based on conversations with a company rep hosted here a while back, I use 1/2 ounce (14.7 ml) concentrate per 5 gallons of cold water; 1/4 ounce (7.39 ml) concentrate per 2.5 gallons of cold water; 1 tsp (4.92 ml) per 1.5 gallons of cold water.
Thanks Brewbama, sounds like that matches up with what I used to use with the old sanitizer at 12.5 ppm. 1/2 oz or 3 tsp for 5 gals. The IO-star has 1 oz or 6 tsp for 5 gals equals 25 ppm. The tsp measurement is not on the label but I Googled it.
On the subject of IO San, I circulate 2 ounces of this sanitizer in 10 gallons of hot water throughout the cold side of my brewery on brew day. When I start the process, the water is a reddish orange color. However, after about 20 minutes, the water eventually turns clear. Why is that and is the sanitizer still working at that point?
The hot water drives off the iodine gas. The mfr specifically calls for cold water. The hotter the water, the faster the Iodine will gas into the atmosphere.
It will do the same if you store it mixed in a keg even if cold but it will take maybe a couple days for it to gas off. I learned this a long time ago from a past experience.
That’s great to know! Thank you!! 
The exception is if the keg (or whatever vessel) is sealed, then there’s no place for the gas to go and it will come to equilibrium pretty quickly.
I prefer iodine over starsan, I think its 99.9% rather than 99% and nicer to deal with other than discolouring plastics.
I use 1.25ml / 1 litre of tap water.
Starsan is annoying because it gets milky strings in it if you use tap water that isn’t very low in minerals and let it sit a day or two.