Hi jeo,
First off - you are in an excellent position to do your 75 gallon tank right the first time, and not have to go back and make modifications later.
Going with the 75 over the 55 - excellent choice.
Sump Refugium - Ideal set up IMO, and much much easier to set up prior to having your tank set up, and having to do later.
29 glass sump would be great if you can indeed fit it under the stand.
If you build your own stand - it may be possible.
Many store bought stands, depending on where the stands door is located, prevent many of us from using a large glass tank underneath for sump/refugium. It just flat out will not fit - I've tried - and the laws of geometry will not allow it. Just not enough room in many cases.
If you set the glass tank sump in the stand BEFORE placing your 75 gallon tank on top of stand - it's possible then.
Sometimes people,including myself, will use a Rubbermaid type container for this reason.
You can get some pretty good size plastic containers for a song, modify them to your needs, and they work rather well. Can't see through them, some may find they look sort of "hillbilly" rigged and unprofessional, but they are removable if you have space limitations with the stand's door.
Pro's of using a glass tank.
Easy to divide into separate chambers with acrylic sheets for dividers/baffles.
Looks cleaner - nice to be able to see what's happening in the sump.
Lots of inexpensive smaller tanks out there to choose from.
Downside of using a glass sump. If it ever develops a leak - and sometimes tanks do - if it won't fit through the door of the stand - pardon the expression ... you're screwed.
Gotta empty and lift off the display tank to get the leaker out.
Other than that - glass or acrylic tanks for sumps are better - again IMO.
DSB deep sand bed and as much live rock in the display tank is the greatest thing for reef tanks since ..... well I don't know - they are both just EXCELLENT things to have, and planning this from the start will be the best advise you'll probably get here.
If you have enough live rock and DSB, most other "optional" biological filtration is just that - optional.
Skimmer's are good if you have lot's of fish - but if you keep your fish load low - you may not need one. Especially if you go with the algae scrubbing refugium.
AS rhomer said, the refugium is used as additional fitration. By placing some live rock and sandbed in the refugium, and allowing macro algae such as caulerpa to grow there - the algae will take up some of the "excess" nutrients in the tank, such as nitrate and phosphate, will help stabalize your pH over time, adds oxygen to the water, and is a great thing to have. As the macro algae grows and removes nitrate/phosphate - some of it is occasionally harvested and removed from the system - thus REMOVING these harmful compounds from your reef system. Mother nature at it's best.
If I were you - I would hesitate setting up your tank this weekend - if you can stand it - and wait until you have all your equipment, stand and such. This will prevent you from having to re-do stuff later.
A HUGE advantage of planning ahead.
HTH and good luck - keep your questions coming.
See ya,
Broomer
