i am geting a new tank next week would you say it will be ok to put the water from the old tank in to the new tank as if it was a water change as the new tank is bigger and whatdo i do about the fish will thay be ok there all hardy fish
using old water won't help one bit, as little to no beneficial bacteria are water borne. instead, you have 4 options on preparing the new tank for use.
1. using mature filter media from your existing filter
2. running a filter alongside the current one until enough beneficial bacteria has formed in the new filter