Hello, I have an undergravel filter, and I just replaced the Air Diffuser for it. My tank just cycled and I am wondering if taking out the old air diffuser will disrupt the cycle and start it over? Should I have left the old one in?
The air diffuser won't affect your cycle much at all, most of the bacteria will be living in your gravel. Something you should watch for though is your nitrates. After a while crud builds up under the filter and your nitrates will start shooting up fast. About that time your going to have to pull up the under gravel plates to clean it out, I'd suggest getting an HOB filter before then.
Just to add to bosk1's post, run the HOB filter along with the undergravel for the next couple of weeks. I'd wait at least 2-3 months or so, to be safe. You need a good amount of time for the bacteria to colonize on the HOB's filter media.