The reflectors seemed to keep the light in the area of the tank, so I decided to go with 10" sides, mainly to hide the fixtures inside. I didn't put gaps between these planks so the light won't leak out, particularly on the ends where the reflector doesn't reflect the light downward. The addition of the sides made the canopy much more rigid which was good.
I wasn't sure where I would put the ballasts. They are heavy, but not too bad. I test fit one along the center brace and the mounting holes aligned with the planks that have the metal supports and eye-bolts. I decided it would support the ballasts and allow plenty of space for cooling.
The ballasts came with jacketed, heat resistant cable going to spade plugs for the light fixtures. With the ballasts mounted so close, I didn't need that much cable but didn't want to try to shorten it in case I needed to move the ballasts later. Due to the special jacket on the cable, it wouldn't coil neatly, so I just routed it neatly around the fixture. It looks like I planned it all from the start!
One last touch was the addition of some more 2x3 along the bottom edge of the side supports. I cut grooves lengthwise on the inside and fit some glass in them. I think it would work, but the glass I bought was simple 3/32" glass which was difficult to cut cleanly, much less install without breaking it. Since the canopy will be so high above the tank I think I'll go without glass for now. It was mainly to protect the bulbs, so I'll keep an eye on it.
It looks good! I added some trim pieces to the ends to cover up the cut corners that were on the fence pickets. I found that the 2x3 I put along the back edge cast shadows on the bog area, in part because I ran out of planks for the back. For now I took off the 2x3 along that edge and I'll wait and see how it goes.
The tank is filled here for water testing purposes. I also wanted to soak out any contaminants that may have been introduced during the build process (the silicone said it was 100% silicone but also said it wasn't for tank use, plus the cut rock panels were glued together with liquid nails.) To help in that process, I'm running the filters packed full of charcoal. In the bog area you can see the beginnings of the slate build. A friend suggested some lattice for the wall with some climbing plants. I used some cedar scrap to mock some up to see how it looked. I think it's worth pursuing.