repetitive questions, sorry...(sump design)

Just some thoughts based off of your questions. The baffle heights do a couple of things. They dictate how deep the water is in each section (I know, obvious right?) so make sure that the skimmer box isn't too deep. I've got a NWB-200 and it likes about 8" of water. Your 150 might be similar and it looks like you are planning on 8" after the 4" stand (which is deceiving due to the 4" stand being not to scale).

The benefits of the "taller" baffles are:
More water = more stability in water parameters
Deeper bubble traps to prevent even more bubbles from sneaking through

I think that the overall design is ok, but as you mentioned, the return pump area is small. This is the only chamber that you will see the evaporation happen in. The DT will stay full, and the fuge and skimmer boxes will stay full. The water will just drop in the return section.

An ATO is great anyway, but be prepared to have a good sized reservoir or be refilling the reservoir often. I am using just a 5 gallon bucket (cheap and easy) for my 120 gallon with a 40 gallon sump (which uses about 20 gallons of water when running) and I have to fill the bucket 3 times a week. That is with a sump that is split into just 2 chambers so the return pump has access to about half of the sump's water.

 

If you are planning an ATO why not simplify the design to get greater size in the refugium? move the return pump to the end with a short baffle just to keep the crud away from it. With that distance from the skimmer you should be able to get away with only a couple baffles before the refugium and the short one dividing from the refugium.

Also, given the footprint of the skimmer, you could likely set in in the first chamber and at angle and get it down to 9-10"s or so.

A million ways to do it...but my first thought:
http://i282.photobucket.com/albums/kk254/mnabryant/sump_zpse3756484.png

 

See, I just point out issues, MJB comes with a solution!

 

I know some people like lots of internal baffles to stop bubbles, however, I don't have a lot of issues with bubbles from my skimmer, so you may or may not want three baffles dividing the skimmer and return pump. Just a thought. But I would listen to MJB as he's dealt with this a bit more. /DesktopModules/ActiveForums/themes/_default//emoticons/smile.gif

 

Well I guess it depends exactly what you are going to put in the refugium. Actually this baffle layout will encourage a majority of the water flow to take place higher up in chamber so the sandbed or whatever you run in there won't be quite as disturbed. Also, assuming you already have the mag 9.5, you could put a valve after the outlet and have a little more control over the flow rate instead of letting it run wide open. For example, if you assume 4ft of headloss puts you at 700 gph (assuming height and plumbing restrictions). If you valve back 25% you'll land around 550 gph or so which would probably work nicely.

As far as the volume in the return chamber, my illustration has it combined with the refugium so it's really a 2 chamber setup with the little partition by the mag drive keeping the pump area isolated from refugium sand or mud if you use it. So the skimmer chamber height is dictated by the second baffle and everything to the right can vary with evap as one chamber. Use he ATO to manage that level where you want it but you'll be able to keep the depth relatively constant that way.

Again, just my thoughts on it to maximize your refugium space.