i am starting my tank and i got a 30 gallong tank made into a fuge but i was wondering if i should use sand or bare bottom and if i should use sand how deep should the sand bed be
Extremely opinionated answers will be given to this question. Really no wrong way to do it unless you try to place a return pump in the same area the sand is in.(use baffles to prevent the sand from getting to the return pump if you uses it, use baffles anyways to keep macro out of the pump or out of drain line if it’s drilled)
If you are going just for function I would go bare bottom Chaeto only. If you want to do something a little different you could throw in some sand and other types of macros as well.
If you choose to use a substrate in the bottom the other option is what type. You could use the standard size special grade aragonite, or figi pink fine sand, or mineral mud, or Brightwell’s new fuge media, or silica sand, or you could fly to the tropics and scoop some sand or mud out of the wild. Couple options. 
I’ve gone bare bottom and never looked back. Love the ease of maintenance.
Good point there.
With decent amount of flow there won’t be much settling of crap to siphon out. Mineral mud is supposed to be replaced once a year. Deep sand beds according to Ken have some sort of maintenance. Bare bottom is nice and simple and idea for chaeto growth which is my favorite at this point for nutrient absorption.
On the same note, a sand bottom is beneficial for its own reasons. If you are using it to cultivate different types of microfauna sand or even the dreaded (by me) light cover of crushed coral can help a lot. There is a bit more maintenance, but that has Never stopped me from making my systems. Just remember, you can always make the flow faster to keep dead space down, and if you do do some type of sand, just keep it under 2" and you will be fine. Good luck!
Under 2" or over 5" of a fine sand for a deep sand bed. I wouldn’t recommend deep though personally, but you will find some that preach it’s benefits. To me risk out weighs the benefits.
In my opinion any type of crushed coral is going to add a significant amount of maintenance. I understand the benefits of maintaining different grain sizes for different “critters” and “pods”. Some people obsess over keeping the rocks off the sand to help prevent nutrients sinks in the display tanks substrate, little rocks on top of your fuge I think would do to the same thing to a certain extent. Consider alternatives if “pod” and other microfauna production is desired:
Crushed coral in an up flow media reactor… potential little to no maintenance if kept out of light.(kind of like a dark fuge) It will cultivate “pods” just like a media reactor filled with carbon and left in the system too long with out the risk of having the carbon dump it’s nutrients after a month. I believe the microfuana would benefit from the slightest amount of light to grow a tiny bit of algae, but indirect only especially if it is a very high nutrient system which most home aquariums are.
My first tank had a plenum with an undergravel filter (hey it was long ago, circa 1988) and a deep sand bed. I had very few problems with that tank. Other tanks were shallow because I like the look of the shallow sand bed and did not want to have to look at 6" of sand at the bottom of the tank. I had more nutrient problems with a shallow sand bed. I think if I had more nutrient absorbers then I would not have had as many issues. If I were to do it again (I will soon) I would go bare bottom for the display to make maintenance easy; besides coraline will attach to everything in a few months and the bare bottow will look rough and have plenty of texture. I would have a larger fuge then I did in the past equal or greater then the volume of the main tank. I would set up artificial habitats for numerous micro and macro-organisms from pods to sponges, I may even include a remote deep sand bed (RDSB). This would allow me to unhook it from the main system to do maintenance and still have the benifits of the DSB
Here is a link to help you made your decision
Both methods work; it’s just what you are trying to create.
[quote=“a1amap, post:7, topic:3464”]
I would set up artificial habitats for numerous micro and macro-organisms from pods to sponges, I may even include a remote deep sand bed (RDSB). This would allow me to unhook it from the main system to do maintenance and still have the benifits of the DSB[/quote]
My plan as well 
Damn- - someone must have hacked Ian’s account >.< No way he’s bored enough to start posting again- -especially since he doesn’t have a tank set up ;D
[quote=“Cdangel0, post:10, topic:3464”]
especially since he doesn’t have a tank set up [/quote]
What happened there Ian? You move?