^^^yeah i found mine through that link, too. very helpful.
it's good you're taking him to the vet, he does sound sick. even though you did the water change, it shouldn't cause such a drastic change in behaviour. i had to do a full water change on my 55 gallon tank, so i had to keep aeryn landbound for almost two hours while i drained, scrubbed and refilled it (i do not have proper tools to do it quicker

) and she made it perfectly clear she was po'ed about me keeping her landbound by nipping at me, and she swam off faster than the dickens. the biggest change in behaviour there was her attempt to bite me.