i wouldnt use a 'water conditioner' as all it does is irritate their skin/scales to create a thicker slime coat. i dont think there is a single fish that cant handle 1tbs/10g of salt and quite a few that will benefit from it used regularly. clown loaches apparently are one of them!!
they are of a family of fish that are considered 'scaleless'. ive kept loaches and used salt with them as an ICH treatment (2tbs/5g) and they were fine but im not sure of the long term use. there is quite a bit of literature on treating them with salt for ICH but very little on keeping them in a brackish or low end brackish system... although a great deal about them venturing into near SW conditions through out their life.
platies do considerably better with hard water and roughly 2-4tbs/10g of salt in their water although they adapt quite well to purely freshwater.
here are some articles for you to read on them-
and your loaches-
and your pleco-
i like www.wetwebmedia.com
for most of the information on fish although i try to use most of the sources i find. if i had to make a suggestion, put the pleco in with the loaches in the 65g and keep a real close eye on the water parameters. if it looks like your nitrates are manageable (ie under 40ppm at the end of the week, resolved down to 20ppm after WC) then see abotu adding a few platies. ive only had smaller tanks, nor have i ever kept a pleco or clowns but a few clowns and a pleco seems like a lot for a 65g. BUT neither species should be kept in anything under a 45g.
if i had to make a harder suggestion, take the laoches back and get some smaller ones.
the loaches ive kept are quite silly little guys and they dont even get a fraction of the size a clown does. yoyo loaches, blue skunk, zebra loaches all stay small also.
oh and one last thing, it is dangerous to net loaches or plecos. they have spines all over the place that can get stuck in the net and become damaged. i prefer to use cups or... well in your case BUCKETS to catch them in. also ive known some serious pleco people who have found their plecos half dried up behind the tank that survived.
moral of the story?? fish are amazing creatures!! just keep up with the water changes to keep the water perfect, your loach should heal just fine.