Celebrating the Awesome Beauty of the Lord's Tropical Reef in a Home Marine Aquarium

Canopy Modification - MH Pendants


Once I had finished the electrical center modification and had the rest of the aquarium components in-place I started the final project to install the metal halide (MH)/very high output (VHO) lighting to the inside of the canopy lid as well as the 5" Orion fans for cooling air circulation.

Here's a list of the lighting components we were installing in the canopy:
- Three HQI 250W DE (double ended) MH Pendants;
- Two VHO 140 Watt Retro Kits; and
- Two Orion 5" AC Fans

Since we went with MH pendants for our main lighting solution, research indicated we had to have about 8 to 9 inches from the MH bulbs to the surface of the water. With the HQI 250W pendants installed on the underside of the lid on the original canopy there would only have been about 6 inches of clearance. Knowing this in advance we had Oceanic custom-make the canopy 3.5 inches taller. Here are a couple shots of the canopy (Pic1, Pic2) just after it arrived from our supplier.

Step 1: Modify the cross braces on the canopy lid to allow flush-mounting the MH pendants.

It is unfortunate that the design of the Oceanic 135RR canopy lid was such that three evenly spaced MH pendants (bulbs centered over each two feet of the water's surface) could not be installed between the cross braces. This step concentrated on cutting out sections from the cross braces on the underside of the canopy lid to make room for flush-mounting the pendants. These braces provide strength and rigidity to the lid, so I couldn't cut the sections completely out. In the pictures (Pic1, Pic2) you can see what the braces looked like before and after I modified them. The width of the cutouts matched the width of the pendants.

Step 2: Design and create a structure that fit into the lid on which to mount (hang) the pendants and VHOs without having to penetrate the outside of the canopy.

A major criterion for me was to keep the outside of the canopy lid in original condition with no protruding crews or hooks. I wanted the entire lighting assembly to be installed on the underside of the lid with no penetration of the external structure. With that in mind I needed to come up with a design that allowed the components to be "captured" and held in place when the lid was in the normally closed position. Mind you, weight of the design was not a criterion since opening and closing the lid to access the tank was not going to be required.

I came up with a design that essentially called for the pendants to be attached to flat pieces of 1/4" plywood that were then fit snugly into the lid and held in place by small variable length 1" x 1/4" strips along the front and rear sides of the lid (Pic1, Pic2, Pic3). Note in Pic1 & 2 that the plywood was cut to fit snugly between the front and rear edges of the lid. Also, in Pic3 you can see the 1" x 1/4" strips in place to be screwed into the front and rear edges of the lid to capture the plywood panels. While this wasn't the lightest design it was sturdy and easy to make.

Step 3: Attach the pendants to the plywood panels being sure to provide a small air gap to keep the intense heat from transferring directly to the plywood.

Another important design goal was to be sure the pendants were attached to the plywood with some type of spacer to serve as a standoff so the pendants did not directly contact the wood. These glass beads came in very handy in that they were the perfect size and had a hole through their centers for the pendant attach screw. I measured the plywood to find the exact centerline parallel with the length of the canopy lid and scribed a line on each plywood panel. I then measured to locate the exact spot where the center of each MH bulb should be (each bulb is in the center of each 2 foot section of the 6 foot lid). With the bulb centers located I placed the pendants on their spots along the centerline and marked the position of each of the pendant's two attach screw holes so I would know where to drill the plywood.

Next I drilled the six attach screw holes (two per pendant) through the plywood and then countersunk the screw holes on the sides that were against the lid so that the screw heads would not prevent the plywood from sitting flush against the lid when installed. Then, on the other side of the plywood where the pendant would be attached I used a 1" Forstner bit to carve out a 1/8" deep champher around the screw holes to provide a place for the glass beads to rest when the pendants were attached (Pic1, Pic2, Pic3) .

Once all the holes were prepared I trial fit each pendant to be sure everything fit well (Pic2, Pic2, Pic3).

Now that the trial installation of the MH pendants was completed it was time to install the VHO Retro Kits.