Hi! My name is Cheyenne, I wanted to get some opinions from some more experienced reefers about filtering a large 120 gallon aquarium. My ultimate goal in this tank is to house primarily EELS! I understand some eat fishies others, your shrimps and snails, but I also wanted to house Garden Eels. Based on my reading through previous threads and a few books with little tidbits of info I understand they need at least 6-8" of sand. Which I am ok with, they are super cute! Problem With Undergravel Filter - My problem is that I plan on having a 20-40 gallon long sump with an overflow to get the suction going, with a skimmer, some good filter-media, and a refugium. With this sand bed though being so tall, I am wondering if a under gravel filter is even worth it to consider? I understand there are layers of the sand where beneficial critters grow, but I don't know how much disturbance it would cause. Plus the more I visualize sand, I think of it like a broken vacuum cleaner, simply falling through the filter to get blown out into the tank and have a sandstorm hayday. Problem With Heating Water - Simple question for this, when using a sump filtration system, I keep reading about reefers who put heaters in the sump to heat the water. How does that even heat in the first place (like have ample time to heat if water is constantly moving) and how do you keep it constant with that in mind? Would you put a heater in the sump and the DT? Critter Question In the book I am reading on SW tanks they mention putting brittle stars in the refugium. I've seen a few brittles that weren't "tiny" persay, but I would be afraid of them escaping and getting very brutally sucked up and spit back out into the DT, but also feel cruel encasing the refugium like a little seastar jail cell. (I know with eels I will have to eel-proof every possible escape but the brittles are innocent! lol) Also, with the refugium in mind, I keep reading about copepods, and hearing both sides of the table of them being good yummy food, and then also bad. So essentially I am doodling in the sand in the middle not sure which side is more accurate. That and I know some critters like their good amount of plankton. Would one recommend to (right after getting nitrogen cycle completed) to start cultivating them? Tank Info - A little more info on my goal for this tank, like I said 20-40 gal. sump, 3 tiers: skimmer, media, refugium, back to tank. Lots of eels, garden and snowflakes are what I would like to start with. Then branch out and "maybe" add some clownfish and tangs (bigger fishes). So far I have about 20-30 lbs of dry rock that is waiting to get cured, but I am still in the early stages of getting my materials. I already have two Koralia pumps and my tank and some dry rock. so I am getting there .-. I am waiting for a nice or decent skimmer to come along in my area on the used side which is whats keeping me so far from setting up my plumbing. My bf and I are building a stand for this giant beast of a tank (I started with a 30 gallon FW tank) but the guy who cut our wood botched the measurements T^T Back to square one with that. So first I would like to thank anyone who reads this rant to start, I suck tremendously at explaining clearly I've been told. Also thanks to anyone who provides insight on this!