It's time to purchase the tank!
What questions should I be ready to answer?
Should the tank be made out of glass or acrylic?
When it comes to tank composition there are literally knockdown drag out fights over which is better. Like my political views, I'll take the middle ground and say that both are great, but each has it's pros and cons, and one needs to decide which inconvenince he or she is willing to live with.
Glass - Pros
Scratch resistance - In comparison with acrylic, glass is much harder to scratch, and assuming that the seals hold, one can keep your glass tank for a very long time.
Cleaning - This goes hand in hand with scratch resistance. One can use razor blades and powerful magnets to clean glass tanks. Try this on acrylic tanks, and soon you'll find that the clarity of the tank will decrease. This is not to say that you can't use magnets on acrylic tanks, but you just need to be careful.
Top access - Glass tanks typically don't require as large bracing on the tops of the tank as acrylic. This allows for more light to actually enter the tank, and allows for better access to the interior of the tank.
Cost - Glass tanks aren't nearly as expensive as Acrylic tanks, unless you opt for PPG's Starphire glass which is a glass-like material that has the clarity characteristics of acrylic.
Glass - Cons
Weight - As mentioned above, this is probably the reason that most people choose not to buy glass for large displays. Since I live in a multistory building, I'm concerned with the weight that I'm putting on the floor. The building doesn't need another elevator shaft.
Fragility - I've read horror stories on the Internet about people waiting months for large custom glass tanks only to find a crack after the shippers had left. It could be a flaw in the glass, poor craftsmanship, poor handling, whatever -- all you are left with is a heavy broken tank, and waiting for the shippers to come back between the hours of 9 a.m. to 5 p.m. What a coincidence! That's when I work too!
Clarity - Real glass has a green tint to it. Not really a big deal in my book, but some people want what they see in the local fish stores which are almost always acrylic.
Modifications - It's important to plan ahead, and have the tank pre-drilled before it arrives on site. If you find that you need to drill, then make absolutely sure that the glass pane that's being drilled is not tempered glass, otherwise your tank will look like the front door of an Urban Outfitters.
Acrylic - Pros
Clarity - Acrylic affords much better clarity and transmittance than normal glass.
Weight - Acrylic doesn't weigh nearly as much as glass does. I'll post some exact numerical proportions when I find some. This is probably the most compelling reason to buy an acrylic tank, and it was mine even the second time around.
Strength - Assuming that the solvent welds were done properly, the acrylic tank is essentially a single pice of acrylic (at east in theory). There isn't a need to worry about a pesky critter, like a mantis shrimp, shattering the tank, or seals that might degrade due to UV exposure.
Drilling - Acrylic is easily drilled for bulkheads. Said differently, one doesn't need to plan out every drilled hole before hand. No need to pay glass drilling experts to drill holes in your tank. Could you imagine having to haul a several hundred pound tank to a glazier, and then bringing it back?
For drilling holes in acrylic read this page.
Acrylic - Cons
Scratches - If you go to your local fish store, and really look hard at the acrylic tanks you'll see scratches, and even some frosting on the oldest of the tanks. It's a fact of life when buying acrylic, so be careful. If you chose to buy a magnet to clean the hard to reach spots, consider the thickness of the acrylic so that you don't buy one that's too powerful.
Cost - Acrylic tanks will cost you about two to three times that of standard glass, but are a little cheaper or about the same as PPG Starphire glass aquariums.
Many reefkeepers try to avoid acrylic, and prefer all glass aquariums; however, for my needs I find that the benefits of arcylic outweigh those of glass aquarium which I will describe below.
Which tank shape and dimensions should I pick?
Reef tanks come in all shapes and sizes, but the most common are rectangular. Hexagonal, cylindrical, and even spherical tanks can be found, but I suggest leaving those novelty items for the terrariums and goldfish tanks. Oddly shapped tanks are difficult to clean in a marine environment.
In the U.S., tanks are often sold in terms of gallons, shape, and whether they are "tall" or not. For example, a 120 gallon rectangular tank may have the dimensions of 48" x 24" x 24" (length, height, width); however, a 120T (tall) gallon rectangular tank would have the dimensions of 60" x 24" x 18". These have the same volume but drastically different dimensions.
Width is the most important dimension for reef tanks
If you are planning a coral reef tank, the most important dimension is the least obvious: width (front to back depth). A wider tank yields more aquascaping possiblities. Most experienced reefers if asked what they could change would say that they wanted a wider tank. At a minimum, twenty four inches should be reserved for width on reef tanks larger than 75 gallons.
In case you were wondering, the least important dimension is height. In fact, the taller the tank, the more expensive the materials are to build it. Tall tanks require thicker tank material in order to prevent bowing and rupture. Tall tanks also require more powerful lighting in order to get the best penetration to the bottom.
Is the thickness of the tank material important
With regard to glass tanks, the thickness of the glass is probably not important if you're not building it yourself. However, for acrylic tanks it's a different story. Acrylic has a considerable amount of tensile strength so tanks can be fashioned out of relatively thing material in order to save on cost.
For most tanks, 5/16" acrylic is used. Unfortunately, when the tank isn't filled with water one doesn't see the amount of bowing and distortion that the water will have on the tank. This bowing is emphasized dramatically on taller tanks which are 24 inches and taller. In order to alleviate this problem, 1/2" acrylic or thicker material should be used on tall tanks.
Thicker walls will prevent bowing on acrylic tanks
If larger openings are desired on the top of the tank, a very thick 1" acrylic may be used to prevent bowing. Most of the rigidity of an acrylic tank is supported in the top. Thinner materials will result in smaller openings on the top which translates into smaller rocks for aquascaping, and less light penetration.
What can I do to save money on the tank?
If you decide that you want a colored background, a way to save a few dollars would be to purchase a colored film. So rather than purchasing an acrylic tank with a blue or black background, you could instead by a completely transparent tank, and then buy an opaque film to cover the back and/or sides of the tank.
Where should my overflows go?
Over flow positioning is mainly an aesthetic thing. If the tank will be viewed from all four sides, then center-center overflows would be appropriate. Most people only have the front side available and possibly the sides. Depending on how many viewing panels are available one could put them dead center or more commonl
Centered - Useful for tanks where all sides will be viewable. These are commonly large rectangular tanks, hexagonal tanks, and cylindrical tanks.
Rear corner - Probably the most common overflow postition is to put it back in one or both corners. This keeps the overflows out of the picture. The overflows may act as a support for live rock.
Rear center - Similar to the rear corner, but in the center. It frees up the rear corners; however, it can cause the center of the tank to become pinched. If used as part of the aquascaping, a rear center overflow can act as a support for live rock.
Side - This orientation puts the overflow completely to one side of the tank which allows only three sides to remain visible or just two if both sides have overflows. This design is ideal for room divider tanks.
How large should the drain be in my overflow?
Typically this question is answered by considering the diameter of the pump that will be used to put water into the tank. A good rule of thumb regarding drains is to pick the next size up from the return pump's input. A 3/4" input will require a 1" drain, a 1" input will require a 1 1/4" or 1 1/2" drain. See the plumbing section for more on choosing pipe diameters.
Drain diameters should be larger than the pipe diameters that are feeding the tank
If it isn't possible to achieve a drain bigger than the input, multiple drains can be used. Under non-flooding conditions, one shouldn't worry about having too much drainage.
A bulkhead will need to be installed in the drain, so if you are drilling the hole yourself, don't forget to leave about 1" around the hole for the bulkhead. This rule depends on the manufacturer of the bulkhead. Always have your bulkheads before you drill because manufacturers may discontinue. It sounds far fetched, but I managed to buy one bulkhead with narrow threading one week only to discover that th next shipment was the new style of thicker threads which nolonger fit into the hole.
Always have your bulkheads before you drill
If you've never drilled your tank before, I recommend that you have a professional do this. If you have a glass tank, definitely find a glazier to cut the holes.