Each DC8 can control up to 8 appliances, it should be enough for a typical tank's pumps, lights, top off feed, heater, chillers etc...
HOWEVER, the DC8 is only rated for MAX of 6 amps per outlet and 15 amps total for 8 outlets, you have to make sure your chiller's start up amp is not more than 6 amps or you will fried the DC8. For those with multiple 400W MH, you will need to stagger the turn on time for each MH so the surge at start up will not blow the internal fuse. For appliances needing more than 6 amps you should use DC4HD which can handle 12 amps max per outlet and 15 amps total draw.