The use of a tripod is almost a must if you want to take sharp pictures. I'd say that the only downside a tripod is its size. Carrying a foot or more long (when folded) tripod is not too much fun and is usually justified with the expectation to see and shoot subjects of considerable interest. And of course "as always" the best subjects present themselves when the tripod was left home.
Tripod use is straightforward - position the tripod in front of the tank, mount the camera, focus, and shoot. That simplicity has some small details that will lead to better images: 1.
If viewed under an angle the aquarium glass distorts the look of the plants. That means that a perfectly perpendicular placing of the camera in regards to the front glass will yield the best results. As mentioned in "Avoiding image blur (1 of 3)" that refers to both vertical or horizontal positions. Here's a picture that was shot with an extreme angle (pointing the camera down at the plants) - you can see how the plants appear "squished" and also not too sharp: 2.
Getting an image of the entire tank requires the camera to be at some distance of the tank. Here's why I state that pretty obvious fact;
Most digital cameras have lenses that allow the camera to be positioned very close to the tank and still get the entire tank in the frame. That's handy but the resulting image of the tank shows some sloping or curved lines. They can be corrected later in Photoshop but the less altering the original picture needs the better.
To get the lines straight the camera lens needs to be zoomed to about normal length. That means that the camera has to be moved away from the tank. Often the distance that is needed is more than the available room and the photographer ends up tucked to a wall or a piece of furniture. Seeing the camera viewfinder may be a problem but also placing the tripod may be a problem or just impossible. If a few inches will save the day you can shorten two of the legs of the tripod so the camera is now flush to the wall or furniture: 3.
Taking extreme macro pictures of parts of plants or say individual Oxygen bubbles requires the camera to be extremely close to the tank glass. By shortening two of the tripod's legs one can position the camera very much flush to the tank glass. Focusing is a challenge and by adjusting the legs' length you can get it just right. Hold the tripod with your hands and gently move it back and forth until you get the sharpest focus. Fix the legs in that position and use the self-timer for best results.
Some features to consider when looking for a tripod: 1.
That is probably the first thing that comes to the mind of the beginner photographer. But nowadays the use of special materials has brought the weight of the tripods to a negligible number and weight is not an issue. Don't be surprised when you pick up a very sturdy looking tripod and it turns to be extremely light. 2.
This is the part of the tripod where the camera attaches. Some camera mounts use a "ball-head" - a term referring usually to more expensive tripods in which the camera is positioned in different ways by fastening a metal ball. Here's an example
Many tripods - especially inexpensive ones - don't use a ball-head but hinges that allow to position the camera in a variety of ways. Here's a picture of an $18 tripod's head:
Expensive or not what you need to make sure is that the tripod's head supports your camera with the heaviest lens you have or intent to purchase. Be aware that some heads slip very slowly under the weight of the camera and lens. In general metal heads are preferred but most lightweight digital cameras should not be a problem for any tripod head. 3.
Tripod size can refer to two things - how high and how low can the camera be mounted. The further apart these numbers the better. Compare these 2 tripods:
Tripod A - allows you to position the camera at a maximum height of 5 ft. and a minimum height of 1 ft.
Tripod B - allows you to position the camera at a maximum height of 7 ft. and a minimum height of 1/4 ft.
Tripod B is the better choice because it's more flexible. As usual that comes with a price (especially the lower minimum height). But for the purposes of shooting planted tanks one doesn't need anything excessive and most tripods do a fine job. 4.
Many tripods have two kinds of "feet" - rubber caps and pointy metallic or plastic "spikes".
The rubber caps allow firm grip on most hard surfaces. The "spikes" are obviously for softer surfaces - for example soil or pebbles. Rubber feet will do well in most situations.
A final personal note - as I have mentioned before it may be worth it to buy a very cheap tripod for $20 or so and experiment with it. For that price you will learn what you like and not like in a tripod and you will be better prepared to look for a more expensive model.