I understand what you're saying about the sump. This tank is in my office and although I've got room to put in a sump, I don't want to add extra furniture. I have been toying with some different ideas about furniture arrangements and things so that may be a possibility. If I do one I'll get a CPR overflow, I'm not ready to start drilling glass just yet.
My 10g has a thin sand bed and I definitely like the look, I scuba dive and no sand is just weird looking to me. Are there a lot of negatives to doing a deep sand bed? I'd like to get at the least the bottom decided on before I start, will make things much easier.
As far as doing an auto top off, I don't have RO
system and don't know how I do that. I've seen some pretty cool set-ups but off the top of my head have no idea how set one of those up.
I'm guessing with the HOB
Filter something moving upwards of 350GPH would be sufficient and then add in the PH's. I currently have an Aqueon 75 on my 10g. It's adjustable and max's out at 300GPH. Plus I've got 2 Koralia Nano's (240) and those alternate. 1 on during the day and then off at night when the other turns off. Kinda like a tidal flow, but without the slack tide.