Outfitting the Glass Box
A lot of things go into the "glass box", or acrylic box if you so choose, so the first thing that should go into your tank is thought. You can just run out a grab the one that is on sale, but unless you get lucky, you may regret your purchase over the long term.
The first thing you need to decide is off-the-shelf or custom built. If you are just getting into the hobby, I would probably steer clear of the custom built units. They are far pricier, and you may very well make some costly design mistakes. If, however, you think you have what it takes (a bunch of money, good abilities as a planner, and a place for a tank that an off-the-shelf unit won't fit), go ahead and get a custom built. Just keep in mind the issues that are identified in the following paragraphs
Size does matter. If you read the introduction, I know you are thinking, "Man, at $50 a gallon, I'll just do a 10-gallon and save a lot of cash." Well, that is not really a good idea. You see, small tanks, particularly those less than 40 gallons, tend to be less stable than larger tanks. I am not saying that nano-reefs, as they are called, can't be done. I am just saying that it is not for the beginner. Get handy with a larger tank and marine husbandry first, before you try to keep a reef in a clear plastic Dixie Cup.
As for dimensions, consider the following: Tanks that are narrow from front to back limit your options for aquascaping. By the time you stack your live rock against the back of the tank, you are often left with the brick wall look, and precious little reef floor to work with. So your typical 55-gallon-everybody-has-one-tank may not be the best bet. For smaller tanks, I am quite fond of the 40-gallon breeder, the one we use as our example setup.
Tank height is also a consideration. If your tank is very tall and narrow, it limits the surface area of the water, somewhat inhibiting gas exchange. This is the case with most "Show" tanks. Another problem with tall tanks is cleaning them. To get a good cleaning, you will be shoulder deep in seawater to reach the corners. So, get a tall tank if you want, just be prepared to get wet.
Now, let's get back to pure size versus dimensions. Just as a 10-gallon may not be a good idea for the neophyte, neither would a 400-gallon. Yes it would be awesome, but it comes with an lot of work. A tank that size could easily consume 3-4 hours a week in scheduled maintenance, plus and additional 4-6 hours a month for water changes. If you really like that kind of work, and you've got the time and money, go for it. Be forewarned though, you could quickly burnout on maintenance and find your $20,000 system up for auction on ebay for $200. In larger tanks, I like the 75- and 120-gallon tanks. They have good front-to-back depth, not excessively tall, and are small enough to be affordable, and reasonably low maintenance.
You also need to decide between glass and acrylic. As with everything, there are pros and cons with either. Glass is heavy, hard to shape, and in larger tanks, thick enough to cast a green-blue tint to the water. It is also cheaper, scratch resistant, cheaper, and scratch resistant. Acrylic tanks can be made in most shapes, are lighter, and are crystal clear. They also scratch, can quickly get expensive, and are not as accessible internally, due to the top plate necessary to prevent bowing. I am a glass man, but to each his own.
To make your final choice on which tank, you first have to answer another question. "To sump or not to sump? That is the question. Is it nobler to suffer the sight of heaters, skimmers, and probes in the display tank, than to add another tank under the stand?" A sump will give increased water volume and stability as well as a place to hide all of your extraneous equipment. The only real drawbacks with a sump are the noise created by the overflow, and the possibility of overflowing on an improperly plumbed setup.
If you decide to use a sump, consider one that is about 25% the size of your display tank, and you use a reliable anti-siphon valve. This helps in flood control if the tank tries to drain. For your sump, you can use another aquarium, but a cheap Rubbermaid plastic container will work just as well. Just make sure that nothing has ever been stored in it.
So now here is the last consideration. Do you want a pre-drilled tank with internal overflows, or a plain tank with a hang-on overflow. The first test is "No sump, no overflow. Know sump, know overflow." So, if you want a sump and you've got the cash, get the pre-drilled aquarium. That is just my opinion.
In summary, my advice is to get a reasonable size tank with good front-to-back depth, and that is not too tall. Think about the maintenance and the "total cost of ownership" before you buy. And don't bother trying to find a tank on the net. The shipping will eat you up. Your local fish store will most likely sell you the tank as cheap as you will get it anywhere. Oh yeah, there is always ebay.
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