If this is your second tank and you still have first you could just pull cycled media or LR?
This with an ammonia source would "speed things up" if that is possible.
Otherwise ammonia (pure ) or shrimp in a stocking your choice.
Nice set up!
Was thinking that but I did have flat worms 5 months ago looks like I killed them all but u never know. Trying to keep any bad stuff out the best I can 3 years now with my 30 gallon up only had them that I know of so not to bad
Red planaria? They are built up to be horrible, but their populations rise and fall with their available food supply. You could hit the tank with flatworm exit after you add the new rock- a spike if any wouldn't hurt, because there's nothing to hurt.