Choosing décor and toys for your tank can be especially enjoyable for the fish owner. What you place in your tank is certainly a matter of your preference. However, there are a few absolute no-nos and some guidelines to consider to keep your tank safe for your fish. The main thing you'll need to concentrate on is giving your fish enough room to move around. Don't plan on filling your tank so full of plants, rocks and reef setups that your fish feel as if though they live in an obstacle course.
You should avoid metal decorations that will corrode, or any other materials that may dissolve or decompose, such as wood. Decorative rocks should be purchased commercially, rather than dug up from the backyard, as they may contain mineral buildups that can be harmful to your fish.
When thinking of plants, remember live plants will require extra care and some fish species may not be able to live in the same tank with the live plants. Live plants may require special lighting, as well.
You'll need to consider your substrate material and make sure it will be able to support the plants you want to place in your tank. Check the pH and GH levels of the water in the tank. GH, or general hardness, refers to the dissolved concentration of magnesium and calcium ions, or in other words, how "soft" or "hard" the water is.
For a good reef setup, you'll need a strong light source, a good wet/dry filter, a hydrometer, a protein skimmer and a variety of corals. For substrate material, use gravel, sand, crushed coral, dolomite, aragonite, crushed shells or marine sand.
For fish hiding places, purchase large rocks or some other object that will not dissolve or release dangerous elements into the water. It should be both waterproof and durable.
Above all, have a good time decorating your tank. If chosen appropriately, your fish will enjoy whatever you decide on, and you'll enjoy the added attraction to the room.