calum- first I believe your tank isn't cycled and possibly over loaded. Clown Loaches(aren't they wonderful

) are very sensitive to high ammonia, nitrites and nitrates. Is it possible to put them back in the other tank until this one is cycled?
Frequent water changes will be your fishes friend all the way through this, adding chemicals isn't always the best thing to do right away(sometimes it hides the problem).
Keep up the water changes and keep us posted as to how things go. By the way...
carol