Question: Tank issues and maintaining health of axie

Hi,

I'm planning on moving my axolotl in a larger tank later today as hers was temporary and is getting to small for her to thrive. The thing is a couple of weeks ago my oldest axie was housed in the larger tank.. and he very, very sadly passed away. I was planning on housing them together...

He passed away from some sort of infection... I did my best treating him and removed him from the tank. I believe that the tank was the issue so I tore it down - cleaning sand, taking out old filter media and adding new media (some established from one of my other healthy tanks), 100% water change and scrubbing down everything.

I need to move my axolotl some times today. The tank has been cycling for over two weeks now, I tested the water and it's perfect.
But I'm concerned that there might be bad bacteria still living in the tank, is this even possible? I'm so paranoid and want to make sure I don't lose her too as my boys death was very upsetting.

Should I use the sub from her tank and take out this sand. I'm not sure about reusing old flooring regardless of the fact that I cleaned it... suggestions??

Any suggestions are helpful

- Chloe

UPDATE: I moved her into the new tank. I'm trying to make sure the water is cool and dark for her so that she isn't too stressed out. I'll be keeping an extremely close eye on her to catch any decline in health as early as possible. I'm gonna keep the tank as clean as possible to prevent any nasties from infecting my girl.

I think you did enough. I would leave the substrate in. As long as you monitor the ammonia (your cycle may need to readjust) and keep the water cool enough, I'm sure her immune system will be able to cope with whatever pathogens are left - there shouldn't be much!