If you want to use an anti ich/whitespot med on the loaches, i would recommend "anti whitespot" by Interpet. It won't harm the filter bacteria or stain the water like that and it comes with clear intructions and warnings etc.
If the loaches are healthy though, i wouldn't medicate them. When i bought my clown loaches, i just quarentined them for 2-3weeks and they were fine, never had any ich on them or anything like that- not all clown loaches are infested with parasites. Quarentining them for a couple of weeks will be a much less stressful way to make sure they aren't carrying anything than medicating them with strong anti parasitic meds when they might not actually have anything.