How to Decorate a Fish Tank
To decorate a fish tank, start by choosing a substrate you like, such as natural-looking gravel. colorful sand, or even just a bare tank floor for a simple look. Then, pick decorations that go with your substrate, such as rocks, plants, and, shells. For instance, if you prefer a natural theme, you might add driftwood and live plants. If you want a playful aquarium, you could fill your tank with neon-colored plastic plants and aquarium-safe novelty items.
Try a colorful sand for a beautiful base. Aquarium sand and comes in a variety of colors, and you can choose your favorite as a base for your aquarium. Light colors do well, as they become almost glittery in water. You can also layer different colors, though keep in mind they will get mixed up over time. Another option is a pale tan sand to make your aquarium look like the ocean. Pick sand for eels, knifefish, and rays. Sand is good for eels because they tend to stay on the bottom. Gravel can cut the eels if it's sharp. Rays need sand because they bury themselves in it. If you have a ray, though, you'll need lots of space for movement, too. However, sand is harder to clean than rocks or gravel. Because it is so fine, you'll often suck it up into the cleaning tube as you clean the tank, though its fineness can also make it easier to pick up dirt off the surface of the sand. Try colorful gravel as a base. Aquarium gravel also comes in a wide variety of colors to add decoration to your tank. You could choose a nice blue to create an ocean-like effect or go for more psychedelic colors like hot pink, yellow, or green. You can also mix colors, as the larger pieces will keep the colors more distinct than sand. In fact, you can purchase gravel that is already mixed. Gravel is a good option for most types of fish, so it's a good option in a wide variety of tanks. Try layering colors for a more interesting effect. Another option is smooth, round gravel in natural colors, which looks like river rocks. Medium-sized gravel is the best choice, although small gravel also works. Don't use large gravel. It can trap things under it, including fish and food. Skip it altogether for a clean look. Most fish don't actually need a substrate. Therefore, if you don't want to put one in, you can skip it. You may find it aesthetically pleasing to have it, but you may also like the simplicity of leaving it off. It's up to you. Also, skip glass pebbles as a substrate. They can break down and create sharp edges. Additionally, they don't have a large enough surface area to help grow the good bacteria your tank needs. Pick rocks to create a theme. Rocks can add a decorative touch to your aquarium. Choose from rocks such as lava rock, quartz, petrified wood, and slate. You can also use red desert rock, honey onyx, zebra rock, ice rock, or rainbow rock. Dark rocks like lava rock or slate create a more serious tone, while brighter rocks, such as pink quartz, will make it more cheerful. Large rocks that many layers and crevices help give your tank dimension. You can also pick rocks that have natural tunnels in them for your fish to swim through. You can purchase aquarium rocks at pet stores. However, you can also pick up your own from local areas, as long as you follow a few safety tips first. Check the rocks for sharp edges. You don't want something that could cut your fish. Make sure to test to see if your rocks are too basic (as opposed to acidic). You can test them one of two ways: 1) Drop a few drops of vinegar on it to see if it foams, or 2) Soak the rocks in water for a few days. Once you've soaked them, test the water to see if it's at the right pH level for your fish. Also, clean up your rocks. Wash them off, and then be sure to boil any rocks you find for a good 10 minutes to make sure you're not introducing bacteria to your fish. Use driftwood for a more natural touch. Driftwood is reminiscent of the beach, in particular, and it can give your tank an ocean-like natural feel. You can find driftwood along rivers and beaches. You might also catch some while fishing at a lake, as well as purchase it a pet store. Check to make sure there's nothing living in the driftwood before picking it up. Wash and boil anything you pick up outside before putting it in your fish tank. Use shells to create a miniature ocean. Shells can also add a natural, beach-like feel to your aquarium. Smaller shells make your fish seem bigger in comparison, while using large shells can help you create a theme, such as an underwater mermaid kingdom. For example, you could use large orange or reddish scallop shells to create a mermaid's "home," by opening up the shell and placing a novelty mermaid in the bottom shell. Seashells mostly come in whites, yellows, browns, reds, pinks, and oranges, so keep that in mind when building your color scheme. You can use some mother-of-pearl shells that come in more brilliant colors. You can find shells along the beach. You can also find some shells along rivers and lakes, though it depends on what animal species are living near there. You'll find many stores also sell a variety of shells. Check for animals in the shell before taking it home. Wash and boil the shells to remove bacteria, and don't use them in in freshwater systems. In freshwater systems, they can add too much calcium or change the pH of the water. Use live plants to add a spark of green. Plants can be used to hide away things you'd rather not see, like the filtration system. Make sure you use a variety of plants, as different leaf shapes and plant sizes will add visual texture to your aquarium. Make sure you don't place all the plants at the front, as you'll block the view. Instead, try using them as part of the background in your tank. Live plants can be used in any type of tank, as long as the plant can survive in that type of water. For instance, plants that can survive in freshwater won't make it in saltwater, but you can use coral and algae in saltwater. One problem with live plants is that they will die in time, which may affect the water quality. However, they can add a fresh look to your aquarium. One benefit of live plants is they consume nitrogen, found in your fish's feces. In addition, they use carbon dioxide and put off oxygen, helping your fish breathe. You can buy aquatic plants and coral at most pet stores. Add more green with plastic plants. While plastic plants may not sound that appealing, many of today's products can actually look quite lifelike. Like live plants, you can use plastic plants to hide your filtration system. You might also try some plants that are about mid-height in the center of the aquarium. Smaller plants can go around rocks and other items. Just make sure you buy plants that are approved for fish tanks. You don't want to place something in the tank that could harm your fish. Use novelty items to create a theme. Most pet stores sell novelty items to add to your tank. You can find anything from treasure chests to plastic divers and mermaids. These items are great for creating a particular feel. You can make your tank feel like the bottom of the ocean with a pirate ship and treasure chest, which also adds a sense of adventure. You could create a fantastical world with tiny fake squid, mermaids, and other fantastical novelty items you can find. Many of these items pertain to an ocean theme, so your choices may be a little limited. Choose items that are made for fish tanks, as other plastics may leach over time. Use ceramic pieces to add art. Ceramic pieces can add an artistic touch to the aquarium, as they can be painted in a wide variety of patterns. You can use ceramic pieces to create a color theme or set a certain mood because they come in so many different styles and colors. Try bright Mexican-style pieces for flair and color. You could even pick pieces that have a nautical theme. Add a few plates at the back as a backdrop to your tank or a vase on its side for fish to swim in and out of. For a bit of class and whimsy, consider a few mismatched teacups and saucers or even a whole teapot if your tank is big enough. Mugs and other similar dishes can also create hiding places for your fish. You can purchase ceramic pieces at almost any big box store or decorating store. However, you should check to make sure your pieces are safe. Any unglazed ceramic piece is fine. If it's glazed, it should be labeled "food safe," "dinnerware safe," or be sold as dinnerware. If it's safe for you to eat off of, it should be safe for the aquarium. Use old glass jars or bottles for cheap color. Another option that you can do for free is to upcycle old jars or bottles. Pick bright colors, like green or blue, which help create a beach-like feeling, as they're reminiscent of beach glass.  Clean them out thoroughly, and remove the label. Make sure you get all the glue off. Then you can set the jar on i's side in the aquarium, making another place for the fish to play in. Glass is best because it won't leach chemicals. Try a blue or green jar, which will add color to the aquarium. Use a background to tie it together. Backgrounds are pieces of plastic that cling to the back of your aquarium. Try a solid color for a clean look. You can also pick background that look like ocean water or sand, for a beach feel. You can find backgrounds at the pet store. Another option is to create your own background. You could buy a canvas or a sheet of paper that is the same size as the backside of your aquarium. Paint or draw a picture on it, then tape it or attach it to your aquarium. Use the background to tie the theme together. Keep the theme going. Use the area around the fish tank to keep your theme going. If you've created an underwater adventure with a pirate ship and treasure chest, add pieces outside the tank that fall into the theme, such as bowl of gold coins, a pirate's hat, or small wooden statue like a ship's mast. Alternatively, if you've played up mermaids, try adding similar touches outside the tank, such as a small mermaid's tail or a shell bra. You could also use the same decorations to carry the theme. For instance, if you use slate rocks in your tank, use a few pieces outside the tank, as well. Tie into the color scheme. Whatever colors you've touched on in your tank, continue it outside the tank. For example, if you've focused on pinks and reds, pick those colors up on the shelves around the tank. You could use vases, candles, knickknacks, or even books to pick up the same colors. You could also use colors that tie into the colors of your fish or coral, such as brightly colored rocks or even fake flowers. Try similar styles of plants to continue the theme. Another option is use plants to carry your theme outside the tank. Obviously you won't be able to use the exact same plants, unless you use fake ones, but if you use plants that have a similar shape or leaf, you'll help draw the aquarium into the room's decor. 
Try a colorful sand for a beautiful base. Try colorful gravel as a base. Skip it altogether for a clean look. Pick rocks to create a theme. Use driftwood for a more natural touch. Use shells to create a miniature ocean. Use live plants to add a spark of green. Add more green with plastic plants. Use novelty items to create a theme. Use ceramic pieces to add art. Use old glass jars or bottles for cheap color. Use a background to tie it together. Keep the theme going. Tie into the color scheme. Try similar styles of plants to continue the theme. 