I've had a 55 gallon (48x12x18) for about a year now. I recently had a large crash in the tank that was due to a lack of oxygen in the water. I initially attempted to set the tank up without a proteins skimmer, which after reading many threads on here is obviously a mistake. I'm running my tank without a sump, using a canister as a refugium type filter. I have a HOB protein skimmer, 2 fluval cp2 powerheads, and a 150 watt heater. I also have live sand and rock in my tank currently for biological filtration and I run carbon. So my question is are there any things that I'm missing that could hurt me down the road, aside from a sump. Trying to avoid another crash in the future.