Treating Cuprazin After Myxazin?

[-FighterFishh]

Hello!
I've recently got a new male betta, and after putting the tank through a 3 day course of myxazin, I've realised he's got a couple of white spots. I bought Cupazin to solve this, but my question is can I treat it straight away without having to use carbon in the filter to get out any remaining myxazin?

Also, a little off-topic, but, how can I make the back of my tank less reflective?
The new boy is constantly flaring at it, so he must see some sort of reflection in it. It's got a black background on it, so I'm not sure if that's helping or making it worse?

Any advice is much appreciated!
Thank you!

 

[ellejay]

Funnily enough my bottle of myxazin arrived this morning! It says on the bottle: "do not use within 4 days of using Protozin or Cuprazin". Don't know if that means only when using myxazin after Cuprazin or both ways round. Not sure about the background though!