I understand that water changes are primarily used to reduce the amount of Nitrate and Phosphate in the water. Now that my tank is cycled when do I start doing those 10% - 15% changes? Do I wait for my Nitrates or Phosphates to hit a particular PPM?
Not needed right now but..........I would get in the habit of doing them on a regular basis. 10 % a week is enough. Part of your regular maintance routine.
You can do water changes whenever you want, there is no rule. I've done water changes just because I was bored, dont need a reason.
Personally I wait till ammonia and nitrite are both dropped to zero then I do my first change, then I change water weekly, regardless of nitrate level (I dont even test nitrate)
Ps - Water changes wont lower phosphates, only nitrates.