Nudi`s EAT sponges.. ( except for blue velvet nudies).
I feed mine phytoplankton, ( kent pytoplex) every other day.
The needing to keep one is..
* feed phytoplankton
* keep water quality good for them to thrive
Then you are good to go!
BTW,
They will not give off toxins when they die, but it can cause a bit of ammonia. ( if one is missing= waterchanges).
Good luck!
Tuna