DIY Sump Design - Please review

As for heater placement...covered with water, good flow, and available space are about the only requirements...

In the 120 g DT system I have 4 heaters located in the area you labeled "bubble trap" and for the SH system is is in the area you labeled pump pit.

As for lighting the sump...I figure as much "???" as I can grow in the sump/refugium is all the more that will not grow in the DT. I reckon that should you manage to grow too much outside of the refugium you could run the risk of fouling out a pump...but that could be controlled by a bit of maintenance...

 

I actually blocked a couple parts of my sump because of the clear vinyl return hose getting algae growth and the skimmer section. yes it's good to grow it there but cleaning the DT is much easier than cleaning my tight-fitted sump, if it affects it at all. The fuge portion gets the light's full attention.