There may be some bacteria on the plants and things, but 99.9999% of them are in your filter.
Yes, the bacteria are a good thing! You can change as much water as you like; I've done 75, 80, even 90% water changes in my tanks on occasion.
What you must never, ever do though, is let chlorinated tap water near your filter. That must be gently (just enough to keep it from being clogged up with gunk) cleaned in the old water you've taken from the tank.
There can never be too many bacteria; as they live on the fish's wastes, only the amount that can live on the amount of waste your fish produce will grow.
Here's the article on the 'nitrogen cycle' that's in our beginner's resource centre that will probably explain it better than I can; http
/www.fishforums.net/index.php?/topic/271928-the-nitrogen-cycle/
Keep on with the questions if you have them, I'm more than happy to help
Yes, the bacteria are a good thing! You can change as much water as you like; I've done 75, 80, even 90% water changes in my tanks on occasion.
What you must never, ever do though, is let chlorinated tap water near your filter. That must be gently (just enough to keep it from being clogged up with gunk) cleaned in the old water you've taken from the tank.
There can never be too many bacteria; as they live on the fish's wastes, only the amount that can live on the amount of waste your fish produce will grow.
Here's the article on the 'nitrogen cycle' that's in our beginner's resource centre that will probably explain it better than I can; http

Keep on with the questions if you have them, I'm more than happy to help