2 GREAT OPTIONS
“20 gallon long”
One of best dimensions for smaller planted aquariums are the 15 / 20 gallon longs.
In Asia, one can find 60cm X 23 X 28 (35 litres/9+ gal) or similar. This tank size fits a 60cm light fixture exactly as well. This tank dimensions gives an amazing ratio for the smaller volume. Having more length for fish to traverse also makes the planted aquarium environment much more interesting. In the US, the 12 gallon long (35.4″ x 8.3″ x 9.4″) is great but does not match with standard lights. The 20 gallon long fish tank measures 76.2 x 33 x 33 cm (30″ x 13″ x 13″).
“40-gallon breeder”
The ratio of shorter height with more depth gives two advantages; it’s easy to light up and has more depth for those serious about aquascaping. Choosing this over the smaller 20 gallon fish tank gives more options regarding planted tank plant & fish selection.
A good sized tank for any serious aquascaper; large enough to give great choice in terms of aquatic plants, yet not so large to become extremely demanding in terms of hard scape & time.
So small?
The only cost item that doesn’t upscale significantly with size is the CO2 system for planted aquarium.
While a fully aquascaped show 20-gallon planted tank with quality parts can cost less than US$400, a 65 gallon (120cm x 45 x 45) can easily reach US$2000. Larger tanks require better lighting for depth penetration, custom built cabinets to hold their weight and can take a ton of hard scape & substrate to fill.
Errors in setup also become very costly to rectify; imagining trying to change the aquarium soil substrate in a 200 gallon aquarium tank vs 20 gallon aquarium fish tank. Remember that if you’re into technical aquascaping, hard scape costs for a certain tank dimension will likely be more than the cost of the tank itself.
Getting a large tank, with few plants and mostly empty space is an open invitation to algae.
For beginners I recommend starting with smaller tank sizes to get a sense of how much the effort it takes to maintain a larger planted aquarium. Every aspect, from water changes, pruning and replanting, to making changes in the hardscape will be easier for a smaller planted aquarium. It is these seemingly mundane things that make all the difference in presentation and health of a planted tank. Smaller tank dimensions also encourage experimentation as mistakes are less costly!
A 7 gallon planted aquarium tank on the left can easily be lit by desk-lamps & other household light fixtures. (<$15 USD) While the 46 gallon tank on the right, with a depth of 18 inches, may require more specialised aquarium lighting fixtures to light well. The BML LED light bar on the larger tank here costs around US$300. It is harder to find budget options for large tanks. Larger tanks can also become very costly to ship.
THINK LIGHTING
Aquarium Lights come in standard dimensions:
In North America, lights commonly come in 2,3,4 feet lengths.
In Asia and other parts of the world, it’s common to see lights that are 45,60,90 and 120cm in length.
It is generally easier finding lights for planted aquariums that fit the standard dimensions.
SQUARE TANKS
Avoid square tanks unless you have a design in mind that makes use of one well. They are hard to compose well. It may take more than one light fixture to light them evenly.
SHORT IS GOOD
Shorter tanks are generally easier to manage. As height increases, tanks are harder to light and also harder to prune/clean. 45-60cm is a good range for larger tanks.
GO RIMLESS
Rimless tanks give a much cleaner presentation. Definitely go for these if available. For larger tanks, low iron glass looks better and is worth the price.
HOW BIG?
Do NOT buy the biggest tank you can afford. Instead, buy the largest tank you can afford to aquascape nicely. This means leaving enough budget for hardscape, CO2 equipment, good substrate etc. It is the later that makes an impact, not just the size of tank. Think of the tank as buying an empty plot of land – unless you have resources to build and develop it, it will remain empty.