I have found all tangs fight no mater what...thats all their is to it, its just if they will settle down and get over it or not. Yes stay away from ones in similar body shapes and color and same family.
you can tr brine in a big clear zip lock bag.. but if one of your fish has ick then all your fish need to be treated not just the one wit visible signs, just because u cant see the ick doesnt mean its not there.
I have never seen my adult 7' kole eat any of my hair algea, It does eat some green micro everynow and then though. I feed mine seweed selects, enriched brine,roe(fish egg),formula 2,plankton and i soak all that in Zoe.