its needs to take that long in order for your copepod population to grow into huge numbers. i wouldnt say you need 100+ lbs though. i have less than half of that in a 90g and my mandarin did just fine. how long has the tank been set up? its always a good sign when you change your filter media, whether it be a powerhead or main filter that you see sometimes hundreds of copepods on the filter pads...but you definately will need alot more than no LR at all...