the 900? thats gonna be a crap ton of flow, i replaced mine with a 600 and my corals are happy as can be.. i dk if thatll be overkill, but i also have a koralia mini...
interested on how your modding this thing, i used to use poly filters every but those became a hefty weight on my wallet, the biocube filters work great regardless.
i dk keep us updated and i hope your biocube brings you as much happiness as mine does.. youll soon realize how overheated it will get with that hood ( i dk if you replaced it or not)