This project took a long time to complete. I guess that's one of the distinguishing characteristics of a hobby.
I mostly finished the stand proper in the spring of 2011 (blog entry), but it took me another two and a half years to construct the hood and finish the trim. In the meanwhile I replaced the original glass tank with an acrylic tank, switched from an all-Tanganyikan cichlids biotope to a heavily planted, low-pH biotope, and went through several iterations of lighting and auxillery equipment related to that migration. This post will just cover improvements to the stand/hood since the first post.
Demise of the Glass Tank
I started with an inexpensive used glass tank from Craigslist. After about 8 months use, I had my only overfilling accident: I was using a python to refill after a water change and neglected to pay sufficient attention. The tank filled completely to the brim then spilled a few gallons on the floor. The floors are concrete, so there was no visible damage, but some water probably did seep into the wall/floor joint immediately behind the tank. That night, about 3 am, we woke up to a sound like a fountain. One tank face had cracked near the top, the water level was down about 30 gallons, and the spray bar was making a lot of noise.
I suppose I'll never know exactly what caused the failure, in particular whether the stand proved insufficiently flat or rigid. The location and shape of the crack suggested that outward bowing force from the water was the immediate cause. After overfilling, I left the water level an inch or two higher than I previously had. And perhaps there was some deformation somewhere due to water infiltration swelling. In any case, after thinking it over, I decided to go with acrylic for the replacement, and ordered one from Tru-Vu aquariums.
Seating the Acrylic Tank
I was very concerned to minimize flexion stress on the new tank, so I seated it on top of a sheet of 1/2" styrofoam. The filled tank has been on top of it for 2 years now, with no visible compression. The acrylic tank rests on its entire bottom, so the weight is well spread out. The glass tank rested only on its edge. I had seated that tank on a strip of 1/4" heavy-weight neoprene, but when I remove the broken tank, I found that the neoprene had compressed to almost nothing.
Hood
The hood is very straightforward: a partial box of 1/4" plywood attached by hinges to a wooden frame that rests on top of the tank. The hood's lower edge is about 1.5" below the top of the tank, so the water surface is not visible. All wooden parts got a couple good coats of outdoor urethane. In addition to splashing, the inside of the hood is a high-humidity area. It's been in use for a year with no sign of moisture damage.
Lights
Originally I just thought to illuminate the fish in the evening; eventually I ended up with a hi-tech plant setup. I've now got 4 48" (54 watt) T5-HO bulbs, each with a reflector, mounted to the inside of the hood. The reflectors are screwed into plywood strips that are epoxied to the inside of the hood, so no fastening hardware appears on the outside. I used the Glo T5 HO kit, and the ballasts hang behind the back of the tank. I'm currently testing using a Finnex LED fixture for more intense area lighting, that just rests on top of the tank under the hood,
Ventilation
The back of the hood was left completely open, so air can freely circulate. But when all the lights are on, it gets quite warm under there, and I was noticing temperature swings of 6-10 degrees F above the thermostat setting. (The ambient room temperature can climb into the 80s during the summer, so it's not just the lights.) I decided to try an evaporative cooling solution. I covered 80% of the open space at the back of the hood with acrylic sheets into which four low-voltage computer case fans are mounted, that switch on and off with the lights. When the lights and fans are off, there's enough passive ventilation to avoid moisture problems inside the hood. When the lights come on, the fans blow outside air over them and across the water surface. The acrylic enclosure ensures the cooling air passes through all of the hood volume. On warm days I lose about a gallon to evaporation. The temperature is very steady within 2 degrees of the heater thermostat set point. A possible enhancement would be to use another thermostat to control the fan speed, but that hasn't yet been a priority.
Bottom Trim
The final piece, installed last week, is the trim around the bottom of the tank to cover the plywood/styrofoam sandwich. By waiting 2 years to install it, I learned something valuable, which is that uncovered gravel around the edges of a tank in a well-lighted room can contribute to noxious algae problems. For a couple of months I experimented with taping cardboard around the bottom of the tank and found that shading the gravel was an important factor in eliminating a persistent cyanobacteria problem. I ordered a single strip of 4" wide, 1/16" thick aluminum sheet from Online Metals, and screwed it into the plywood. I was lucky enough to get access to a sheet metal brake to make the bends.
Under-tank space is cramped, but I've managed to stuff in two large canister filters, a 10lb CO2 tank and control system, a UV sterilizer (Aqua brand this time), and the lighting control timer.
