Hi Heldy
It sounds as though you're in the process of doing a fish-in cycle of your tank (i.e. you bought tank and added fish before it was fully cycled - there are notes pinned on the forum re how to fishless cycle btw). But anyway, the thing you will need to be doing now (sorry if you know this already) is regular water changes.
If you can purchase a liquid test kit that would be a great help to you at this stage. It will help you understand the condition of your tank water and how each reading affects your fish.
If your fish get stressed by the toxins in the tank water, this will lower their immune system and then they end up with various diseases - such as this ICH, or bacterial infections etc.
So, if you can do a daily water change of about 15% (let's say a washing up bowl size if that's easier to determine, or one bucket). To reduce further stress, make sure the water is not freezing cold when you add it - try to get it as near the tank temp as poss (if you have a combi boiler that takes water from the cold mains then you can use from the hot water tap, if not you can add a little boiled water to your bucket of cold to get the temp right). Then add your dechlorinator.
By doing these regular water changes you will reduce the amount of dangerous toxins in your tank. Once your filter has built up enough of the good bacteria to convert the dangerous toxins into harmless chemicals, then you won't need to do such regular water changes - they can then be dropped to once per week. And a monthly gravel vac and filter sponge sloosh (in a bowl of tank water) is recommended.
All of this hard work will pay off because your fish will be happier and healthier!
As they say - prevention is better than cure!
Did your LFS tell you that your clown loaches can grow to over a foot long? I think at some point in time you will need to rehome some - that's if they survive to adulthood - they are notorious for getting ICH because they are so sensitive to changes in water chemistry. Not really fish for beginners, to be honest. Never mind - let's hope they all pull through this bout of ICH. They are cute little guys to have in the tank, I know (even though they don't stay little forever LOL).
Sorry if I've rambled a bit but when you are just starting out I think it's good to get as much advice as possible - I know I would have appreciated help at the beginning, rather than learning the hard way
Good luck - Athena