Filter Cleaning

So, 50 days fishless cycling tank, and now 9 days with two handsome platys, i am reluctand to clean my filter for fear of getting rid of much needed bacteria. My filter it is sort of wire wool/fleece with loose plastic pasta bits (K1 media) underneath and stretches across full lenght of 24" tank as it is trickle filter, so all the gunge and goodness may be at one end. How will i know when it's ready to be cleaned,? and how often should i do it after that? i haven't really looked at it as it is the home of the sacred bacteria i have tried so long to cultivate lol

All fine at the mo, so thanks, will leave well alone, build up as much as i can