My group of 10 plus clowns have been a bit twitchy recently which I believe is a type of internal parasite. Tank is 400l and water is kept clean introduced some new loach recently which may have been a host. I don't like to use meds on my loach as they don't do to well with normal fish meds. What is the best clown safe medicine I can get in the UK. My loach are all fairly large 3 inch plus