If the media stays wet whole time then there's no harm to the beneficial bacteria. Beneficial bacteria sticks onto surfaces and will adjust to the parameters as decrease with less of a food source and increase with more food. I do 85% water changes all the time and never have ammonia or nitrite go up not even by .10 ppm and thats including draining the sump. The water doesnt have to be treated with bb at all for 100% water changes, you just have to keep the filter media wet during the water change and match the temp/ph then theres no foul done to the fish or the filtration. Many members such as my self do over 75% water changes and never get a cycle.
edit typooo lol
nice explanation daniel .

is green.

