is it a reef only or with fish?
If with fish I would exchange the crushed coral for sand,CC is a nitrate haven.You need to cycle your tank(fishless)If your putting LR
in the tank you could get away without a skimmer as long as you keep up with PWC
,personally I would use a skimmer if you have fish.For reef tanks you'll need at least 10 x water flow(300gph,this includes powerheads,skimmer,filter)
The filter will need cleaning each week,which is why a lot of people use more LR
in sumps and loose the filter.