Let us be clear on something please.
OP spoke about a foul smell. This is ammonia in my book. ( if it is a fishy smell it may be something else ).
Most proably tank is not conveniently cycled and a large water change with cleaning of bio cartridges has compounded the problem.
So let us get back to basics:
Do not touch your bio media.
If possible get cycled media from a friend or trusted LFS and add it to your system.
Do small, daily wc's. If you do big ones, you will never complete the cycle.
As to HITH, there are several ways to cope with that, but first you need to stabilize the tank.
Is the O feeding? is its poop normal brwon or stringy white poop.
If repply to to both above questions, there is no particular hurry.
Do you have access to Epsom Salt? if you do, do a 3% solution ( half lire of water with a tablespoon of Epsom salt ) and soak the pellets in that solution. Do not drench them. Just let them imbibe for say, 10/ 15 minutes, the solution, and feed. It will start cleaning the fishe's gut of the parasyte.