I am in the process of setting up a 600 gallon fish only salt water tank. I am debating whether to use a wet dry system or a sump. I have a 90 gallon acrylic tank I could use to make the sump or the wet dry. I have live rock from a 200 gallon tank which is being taken down and could be used in the sump. Also this tank will have a closed loop system, I would like to use live sand on the bottom but am considering using crushed coral so that the sand does not get sucked up in the pump of the closed loop system. The aquarium has an artificial reef system built within the tank so putting live rock within the tank is not really an option, I also am incorporating a very large protein skimmer any advice.