+1 on the syringe. I've got one for pretty much anything I mix like Iodophor, StarSan, BLC, fuel stabilizer, 2cycle oil, etc. The graduated medicine ones are nicest. Lest you be perceived a drug addict though, buy them in baby isle at the pharmacy. I make a sleeve to attach each syringe to the supply bottle it's used with by taking a short length of packing tape and wrap it semi-loosely BACKWARDS (yes, that's sticky side out) around the syringe, stick it to bottle where you want it, and then go over that with length of packing tape the wraps around the whole bottle. That way you've always got the right dispensing tool to mix up a batch. BTW, I came up with this technique because I was always loosing those little tubes on the WD40 cans. Haven't lost one of those in 10+ years now!
Oh and metering pumps sometimes called ratio pump, like the one shown earlier are nice too if you have a gallon or bigger supply bottle. They're easiest to fine where ever 2 part paints, epoxy resin, and fiberglassing supplies are sold. Marine supply stores will always have them.