Since the combined flow to the sump directly below the tank should be around 1200 GPH, would this be too much flow for a refugium housing only Chaetomorpha?

<No, that is fine for the Chaetomorpha, but you will not be flowing this much.> I am considering a sump with no substrate because I have heard that the substrate can become a nitrate factory. This is confusing because I have also heard that Deep Sand Beds are denitrifiers. What are your thoughts regarding refugiums without substrates? <I like and use the DSB method. Substrate can become a nitrate factory when it traps excess detritus, usually a trait of large grain substrates. The use of fine substrates will not be an issue and will benefit your system with proper water flow, which you will need even if you leave the refugium bare bottom.> My plan is that the Refugium and the skimmer would be the ONLY filtration in this tank. <And the live rock in your display.> I thank you in advance for any help you can offer. Keep up the good work! Bart <Welcome, will do.  more

<No, that is fine for the Chaetomorpha, but you will not be flowing this much.> I am considering a sump with no substrate because I have heard that the substrate can become a nitrate factory. This is confusing because I have also heard that Deep Sand Beds are denitrifiers. What are your thoughts regarding refugiums without substrates? <I like and use the DSB method. Substrate can become a nitrate factory when it traps excess detritus, usually a trait of large grain substrates. The use of fine substrates will not be an issue and will benefit your system with proper water flow, which you will need even if you leave the refugium bare bottom.> My plan is that the Refugium and the skimmer would be the ONLY filtration in this tank. <And the live rock in your display.> I thank you in advance for any help you can offer. Keep up the good work! Bart <Welcome, will do. Scott V.  more