Here is how I have made moveable shelves that stick to the inside of the aquarium glass. These have worked out so good that I have to be careful that they don't become permanent fixtures in the tank! If you are using frag plugs, this shelf works perfect with them.

Material List
1-Cleaner magnet (get a cheap one that is strong enough to stick to the thickness of your tank glass) Cost: ~$10 from Petsmart

1-chunk of florescent lighting grid (comes in 4' X 8'sheet)

1-piece of thin plastic (1/16" to 1/8" is thick enough) EDIT: if it's too thick, you will have to get a more powerful magnet!

Glue for plastic - (something that will actually melt the plastic like PVC glue)

Saw to cut the plastic and grid. I use wire cutters to cut the grid.

Cut the grid to size....3" X 9" is a good sized shelf

Next remove the scouring pad from one of the two magnets...this is the magnet that will be in the tank water. Scrape it clean and flat as you want it to be sealed when glued to the plastic back. Do not remove the pad from the other magnet that will be on the outside of the tank.

Cut the plastic backing to the width of the shelf grid and the magnet width + 1/4". For instance: The shelf width is 9" wide. The magnet is 1.5" X 3" in size. The plastic backing is cut to 1.75" X 9".

I got a little fancy and cut this piece with some contours:

Next, glue the edge of the grid onto the longest edge of the plastic backing at a 90 degree angle (can use clothespins as clamps):

After the grid glueing had dried, glue the magnet under the grid (clamp down while drying so that there is a good glue seal:

Finished shelf:

Here is it attached to the tank...almost looks like it is floating. Just be careful when cleaning the outside glass....if you knock the outside magnet off, the shelf will fall to the bottom in slow motion!

After a couple months, coralline will start growing on the grid and cover up the white plastic:

Metal halide has long been the industry standard for high intensity reef lighting.  It is a proven lighting solution that can support any lighting needs in a reef tank.   Although metal halide lighting has such a great reputation, it also does have some weaknesses.  High Output T-5 lighting is the new kid on the block, but it has proven to have a few significant advantages over metal halide.  This article will discuss the pros and cons of each of these reef tank lighting systems.

What Metal Halide Lighting Does Right

Metal halide lighting has an excellent PAR rating and will penetrate deep into the water column.  Because the light from metal halide bulbs originates from a single point, it casts shadows in the tank similar to the sun and produces the much sought after "shimmer effect".  It has a long standing track record of being able to support all types of coral life.

What Metal Halide Lighting Does Wrong

Uneven light distribution - Metal halide reef lighting comes from a single round light bulb or a series of round light bulbs.  These bulbs represent a single source of light just like the sun.  Because of this light distribution can be a bit uneven with a metal halide system.  This is one of the weaknesses of metal halide - it almost always leaves a more intense light in a cone shape directly under the bulbs.  This leaves dark spots between the bulbs and can sometimes create a "cone of death" where the light is too intense for most corals.

It gets HOT - Metal halide is very intense and the amount of heat generated can be quite surprising.   In my opinion, this is one of the biggest problems with metal halide lighting.  It will not only make your fish room hot, but it will also raise the temperature in your reef tank significantly.  This often leads to the need for an aquarium chiller to control the heat in the reef tank.  Also, with the heat of metal halides, there is an increased risk of fire.

It is inefficient - with rising energy costs it is becoming increasingly more important to increase energy efficiency.  For a 125 gallon reef tank, it requires at least 750w of metal halide lighting to produce enough lighting to keep SPS corals.

It lacks actinic - In a display tank you will want to add additional actinic lighting.  This used to be accomplished with a VHO setup, but is increasingly accomplished with a few T5HO bulbs.

Poor bulb life - Metal halide bulbs only last about 9 months of normal use.

What High Output T-5 Lighting Does Right

Even light distribution - Because T5 bulbs are long tubes, they spread the light evenly across the tank.  This gives a much more uniform light distribution.

It gets LESS hot - High output T5 does get hot, but nowhere near as hot as metal halide.  Once I switched from metal halide to T5 on my reef tank, my average temperature dropped 4 degrees Fahrenheit.

It is more efficient - High output T5 is one of the most efficient lighting types available for reef tanks.  Some of the new LED systems are much more efficient, but they have not been tested long enough to prove long-term viability and growth.   To grow SPS corals in a 125 gallon reef tank it only requires eight 54w bulbs.  This works out to 432 watts of energy, or a 39% energy savings.

The color temperature choices are vast - There are so many choices when it comes to high output T5 bulbs.  You can mix and match to get multiple actinic wavelengths as well as 10k/14k/20k spectrums of light.  You can really fine tune your high output T5 lighting to maximize the beauty of your reef tank.

Long bulb life - High output T5 bulbs can last up to three years under normal use. 

What High Output T-5 Lighting Does Wrong

Tests for high output T5 lighting have shown that it is not quite as good at penetrating the water column as metal halide lighting.  The PAR rating is not quite as good so corals towards the bottom of the tank may not get all the light they need.  Also, there are a maximum number of bulbs you can crowd over a tank so there is an upper threshold to the maximum number of watts per gallon you can put on a high output T5 lighted tank.  Finally, because the light comes evenly distributed, you all but lose the shimmer effect that is so popular.  Most people like the shimmer effect, but there are those who prefer to have no shimmer effect at all.

Conclusion

We at Reef Time have concluded that high output T5 has proven itself to be a viable reef lighting system.  It runs a lot cooler than metal halide, is more energy efficient and has a vast array of color temperature choices.  Unless you just can't live without the shimmer effect or unless you have a very deep reef tank packed with corals that have high lighting requirements, it is our recommendation to choose high output T5 lighting.