I use both kill coil and biocide in my loop but the catch here is that all my components in my loop are specifically copper - if you check out my sigged rig, Rig 1 - Lutfi's AMS. I don't use dyes and I've flushed my rad with vinegar and water in 20:80 vinegar:water mixture to flush all the components. I also flushed it all with only distilled after the vinegar flush.
The issue I mentioned is when you'll go for something else in your loop like nickel. They tend to corrode under certain conditions and EK specifically say in their disclaimer that you need to use their coolants and not with a silver kill coil for their nickeled blocks. If it corrodes/chips and adds itself to the loop - literally you void your warranty and they can pin it on you for consumer misconduct. So in the long run going for a copper only loop would help you more than two fold.
Most of the havoc threads you read about chipping/blue-ing of clear fluid/damage to blocks/gunked up channels in blocks are from those that run copper/brass and nickeled parts. You mentioned EK supremacy so I assumed what everyone goes starry eyed about - their nickel blocks. Sorry if I've assumed wrongly.
Consider shipping and you'll figure out if you should go for bottle or concentrate on pastel and the dye is a no brainer actually
If you're going concentrate you'll need to drain all the current liquid in your loop, flush thoroughly and then make a batch of pastel and then fill+prime your loop.Edited by Lutfij - 10/4/13 at 2:31pm