Tank Selection

Selection of your tank to start your reef can be one of the most important and expensive decisions that you will make in this hobby.   There are several important considerations including the material, size in gallons and basic dimensions of the tank.

Tank Material:

Reef tanks are constructed of either acrylic or glass.  Both types of tank construction has advantages and disadvantages which are listed below:

Pros of Acrylic Compared to Glass

  • Acrylic is very light weight.  This makes it easier to move when empty which can be important for large tanks and the final installation will be slightly lighter as well.
  • Acrylic is more transparent than standard glass.  Large glass tanks tend to have a greenish tint to the glass unless special and fairly expensive iron free glass is used for the front pane.  This is sometimes called Sapphire glass or other brand names.  I personally would not consider a large glass tank that did not use iron free glass on the viewing sides.
  • The back or sides can be made out of black or other colored acrylic if desired.
  • Acrylic is a better thermal barrier than glass which is a pro if you are trying to heat the tank or minimize the effect of the room temperature fluctuations on the water temperature, but it can be a con when it comes to trying to cool the tank since less heat is lost through the acrylic if the room temperature is lower than the water temperature.
  • Acrylic is less likely to shatter catastrophically if it takes a hard blow or a nail is shot through the side of it with a nail gun (don’t ask me how I know this).
  • Acrylic has no RTV glued seams that may fail over time as the acrylic is chemically welded which is a process that actually melts the acrylic to form a bond as strong as the acrylic itself.  However all bonds are not of the same quality and it is still possible for the bonded acrylic pieces to separate if the bond is not well executed.  Typically a poor bond in the acrylic seam can be determined by looking for bubbles in the seams.  A few small ones won’t affect the strength, but many small ones in an area or large bubbles can absolutely weaken the bond.
  • Acrylic is much easier to drill for plumbing hookups using standard wood hole-saws.  While glass can be drilled, there is more risk of damaging the tank and it is generally done by the tank manufacturer.

Cons of Acrylic Compared to Glass

  • #1 problem is that acrylic can be easily scratched when cleaning the inside of the tank or if the live rock tumbles and hits it.  Similarly the outside can also be scratched accidentally.  Even normal cleaning will slowly create small scratches and all acrylic tanks will get covered with small scratches over time.  This are generally not too noticeable as long as you avoid accidentally getting a piece of sand or coralline algae between the cleaning device you are using and the acrylic which can cause large scratches.  Scratches can be removed by sanding and buffing, but it is generally only practical once the tank is empty though there are kits you can buy to do this with water in the tank which might be helpful in removing a particularly large scratch that you get.
  • The acrylic tanks will typically have wider bracing on the top of the tank, both around the perimeter as well as cross bracing.  This can somewhat limit access to the tank and partially block lighting in some areas.  For instance if you have a 6″ rim on a large tank, you have to reach around this rim to clean the tank which means that you can’t reach as deep into the tank when cleaning.
  • Acrylic can have a noticeable bow on longer tanks depending on the thickness of the acrylic that is used.  This isn’t a concern other than for aesthetics if you are looking down the length of the tank.

Costs differences between acrylic and glass depend largely on the size of the tank.  Small tanks are always cheaper when using glass.  As the tank size increases, the cost advantage starts to swing toward the acrylic tanks.  Typically this occurs once you go above a 180 gallon tank size which is the largest standard glass tank, though acrylic prices have been coming down over time.

Tank Size

This is a major decision point when setting up a reef tank that will dictate many of your future decisions. The conventional wisdom for reef tanks is the bigger the better. Unfortunately, the bigger the tank, the more expensive it is to setup and the more expensive mistakes tend to be. On the other hand if you go too small, you will quickly outgrow the tank and it can be a little more touchy to keep consistent water parameters due to its smaller water volume.

For aquascaping reasons, you typically want a tank that has both some height to it as well as depth front to back.  Think short and fat vs. long and narrow when the tank is viewed from the top.

Locations to put the reef tank also have an impact on the final selection.  Typically you do not want to place the tank where it will get any direct sunlight or be close to a heating or cooling vent.  When going large, the weight of the tank can start to become a consideration especially if you are on the upper floor of an apartment building.  Many apartments have fish tank size restrictions.

20H Reef Tank

                          20 Gallon Reef Tank-End VieW


Smaller Size Tanks

For someone who wants to get into the hobby in a small way either due to finances or not yet sure if this is what you want to do with your spare time, it is a good idea to start with a smaller tank to get your feet wet (figuratively speaking) because if your feet are literally getting wet, then you have done something wrong!  Smaller tanks can also be interesting in their own right for advanced aquarists.

For a standard glass tank from your local pet store or supermart, a 29 gallon tank is a good size. It is big enough to house a reasonable array of livestock, and is fairly easy to light because it can use 24″ long fluorescent tubes or a single metal halide or LED fixture.  It is also tall enough to give some vertical feel to the reef.  The 20H gallon tank is also a nice reef tank size though lighting is a little more limited due to the shorter tank length.   The 20L gallon tank may look a nice option since it is 24″ long, but its short height makes it hard to aquascape for a reef though it can make a nice lagoon type tank.

The tank shown to the right is a 20 gallon ‘high’ tank that I used as an office tank.  The tank had an acrylic divider glued across one end to make a built-in sump which contained the heater, small skimmer, carbon and return pump for circulation.  Slots in the acrylic served as the overflow.  Having the sump hides the equipment plus it keeps the water level in the main display portion of the tank at a constant level.  This picture is actually taken from the end of the tank opposite the sump.  If you enlarge the picture you can see the overflow slots and return nozzel.  The partition created about a 16 gallon viewing tank and 4 gallon sump.

Custom and semi-custom glass tanks are also available in many different sizes.  Rimless glass tanks are becoming fairly popular and a rimless tank in a square configuration such as 18″x18″x18″ can make for a very nice display tank with great aquascaping potential.

For acrylic tanks, there are a number of standard all-in-one tanks available in the 8-30 gallon size.  These can be a convenient starter tank as they include some of the equipment, but they tend to be more expensive and frequently the equipment such as the lighting needs to be upgraded for anything other than a low demand system.

Nano Reef tanks are also becoming fairly popular.  These are tanks in the 1-8 gallon range.  The small size makes them popular as desk tanks.  Their very small size though makes lighting, filtration and maintaining water stability difficult and therefore not a very good choice for someone just starting out.  Some experienced aquarists enjoy the challenge of keeping Nano tanks.

A major consideration when starting with a small size tank is that you should be prepared to upgrade if the reef bug really bites you as you can quickly fill the small tank with livestock and have no place to put that next great coral that you saw at the  petstore.


Medium Size Tanks

70 gallon reef tank

                                                             70 Gallon Reef Tank



A moderate size standard retangular tank that works well is in the 70-75 gallon range. This size of tank usually has a width of 18″ which allows for good aquascaping of the reef. It is large enough to build a decent long term reef that you will not quickly outgrow unless the reef bug bites hard.. The common 55 gallon size will work, but since it is only 13″ front to back,  it does not allow for as nice of a reef structure to be built.

Moving up a notch, the 120 gallon size tank is a very nice size for a reef. It is 4’ long x 2’ x 2’. The two foot width allows for great aquascaping and the two foot height allows for a nice tall reef structure while still being manageable to get ones hands down to the bottom of the tank to do maintenance or arrange corals. Being four foot long, it is generally easier to find a spot to put it than with a longer tank. It is also at the upper end of what 2 MH lamps, 2 LED lights or 4’ fluorescent lamps will adequately light. It is also at the point in tank sizes just before you have to start giving serious consideration to floor loading. A 120 gallon tank will weigh in excess of 1000lbs.

Square or other uniquely dimensioned tanks are available in these gallons as well, though having a location to place a square tanks start to become a consideration since on the larger square tanks, you often want to view all sides.


Go Big or Go Home

For large tanks, there are some basic considerations to keep in mind.

  • Large tanks are typically 6′ long and longer.  A good minimum width front to back to consider on the larger tanks is 24″ and minimum height of about 24″.  One approach is to keep a 24″ height and width and extend the length out. Up to 8 feet tanks are common. Once you go past 8 feet long, the price tends to go up rapidly.
  • If the budget allows, a wider tank front to back is almost always better than a narrower tank.  A 30″ width is a great size and some people go up to 36″ or wider if space and budget allow for it.  This opens up aquascaping possibilities greatly as you can start thinking more in terms of 3 dimensions instead of 2.
  • You have to be able to physically get the tank in the house.  Door widths are usually the first limitation that you need to consider.
  • Taller tanks tend to look nice especially for high demand SPS coral tanks where the corals have space to grow high, but consideration has to be given to how you will service the tank. Once you can no longer reach the bottom, this suddenly becomes difficult. If you are planning on using a DSB (Deep Sand Bed), which is typically 6″ or so deep, this will take up that amount of tank depth and you may want to go with a deeper tank than you normally would to compensate. Another thing to bear in mind is that the higher the tank, the thicker the glass or acrylic needs to be and hence the more expensive the tank will get.  24″ high or less is fairly easily serviceable.  25-30″ starts to become more difficult depending on how long your arms are and over 30″ requires some significant thought before considering tanks that deep.
    225 gallon reef tank

                                                            225 Gallon Reef Tank



  • Taller tanks require higher intensity lights to provide the same amount of lighting to the bottom of the tanks.  This can be a good thing where you can have light loving SPS corals in the upper part of the tank, and lower light LPS corals in the bottom of the tank.
  • Wide tanks front-to-back have a similar consideration.  While a 4′ wide tank may make for an awesome landscape, you have to consider how you are going to reach the back regions of the tank for setup and maintenance.
  • Weight is a major consideration on large tanks.  Pretty much everything that goes into a reef tank is heavy starting with the tank itself, the water at 8lb/gallon, rock, sand, etc.  A 180 gallon reef tank can easily weight over 2000lbs once fully loaded.  This generally means that the large tanks must be on a solidly supported floor whether on a concrete slab or near a wall with some addition support provided for the floor joists.
  • Servicing becomes more difficult.  The larger the tank, the larger the water changes, the more RO/DI water that is needed, the more glass to clean, etc. etc. etc.
  • When something goes wrong, it can be more difficult and expensive to correct due to the size of the system and the difficulty of catching fish, etc.  On the plus side, the larger size generally makes it less likely that something will go wrong in the first place since the system is inherently more stable.