Re: Diagnosing your fish illness -
#7
Definately, a 10L tank is far too small and 'too much waste' probably means high ammonia which is highly toxic. Do daily water changes of 10-20% and consider getting a much larger tank. You will also need to treat the fungus with something like esha2000 but not at the same time as the WS3. Esha claim you can use esha exit for whitespot while using esha2000 for the fungus. I have not read such a claim from king british products.
Also consider getting your own liquid based test kit too so you can do the tests yourself and post the results for ammonia, nitrite, nitrate and ph. This really is required for successful fishkeeping. If you do get the lfs to do your tests get them to write down the actual values for each chemical they test for not just summerise.
In 'the beggining' I used to ask the lfs to test the water they charged 50p per test (so £2 for all four) and always said "its fine" even when my sons first fish keeled over from what I now know was ammonia poisoning.
I didn't realise that for £15 I could buy the api mini master kit and do a years worth of weekly tests myself whenever I wanted.
sorry its a little rambling, its late but I hope it helps!
PS. Welcome to the site!