New Tank, New Filter? Or Can I Use The Old One?

[Lisa67]

I have a 72 gal tank that has been housing mbuna cichlids for several years. For whatever reason they became ill (their bellies became concave), and slowly they have started dieing off. Now, I'd like to try something new (either angle or discus fish) in that tank. My question...I'm not really sure why the mbuna became ill. I'd like to use the same filter as it is still cycled and I really don't feel like going through the 5 week process again (not to mention the money). Is there something I can put into the tank water to kill off anything that may have made the mbuna sick?

As always, thanks for your advice!

 

[the_lock_man]

Is the tank currently empty?

 

[Lisa67]

Yes, keeping it cycled with ammonia.

 

[the_lock_man]

In that case, the chances are that the ammonia will be killing off whatever it was that caused the mbuna illness, especially if you're giving it a high dose.