When I had to QT I had to start before the cycle was complete and I had major ammonia and nitrite issues. I changed 2 gallon out of my 10 and 3 gallons out of the 15. Definitely no fun, but it cured the ich. Now I keep my 10 gallon running all the time just so I don't have to worry about the cycle. I was also told I could use ammonia detox to help, but I don't know how well it works and what effects it would have with the hypo.