undergravel filters

A closed loop seems like a rather good idea to me (I have zero reef experience btw) but I would think the chances of a fish or invert getting sucked up is pretty high. To get past this could an under gravel filter be repurposed to stop anything getting into the pump? Just so there's no...

I built a 180 g saltwater tank about a month and a half ago. I have a weipro protein skimmer, wave maker, and two cannister filters(one sun sun and other dophin),two powerheads connected with an UNDERGRAVEL FILTER. Yes, the person who was helping me building the tank put it in. I have 1 sailfin...