Change the Water

• A partial water change is a "quick fix" that will dilute the tannins. About 25 percent of the water should be changed at one time; larger water changes can stress the fish. This strategy is best for temporarily improving the color of the water, but the problem is likely to come back.
  
  

Take Care of Driftwood

• Certain objects commonly used as tank decorations, like driftwood, may leach tannins into the water. Remove all driftwood and soak it for one to two weeks in clean water, or boiling it for an hour or two. It should help permanently remove tannins. Another option is to seal the driftwood using an aquarium-safe polyurethane sealer. Remove any attached plants such as Java ferns or Java moss first. Allow the driftwood to dry completely before sealing, and again after sealing---do not put uncured sealant into a tank with live fish.
  
  

Add a Carbon Filter

• Activated carbon, also called activated charcoal, is the most widely used form of chemical filtration. The carbon contains microscopic nooks and crannies that trap all sorts of chemicals indiscriminately in a process called adsorption. Use pre-made carbon cartridges designed for your filter, or activated carbon labeled for aquarium use. Place it inside a mesh or felt filter bag in a place with good water flow. If you have a canister filter or hanging box filter, place the carbon directly inside. If you have an undergravel filter and cannot get carbon cartridges for it, you may need to obtain an inexpensive power filter for the carbon. Rinse or soak the carbon first, preferably in distilled or ionized water, to remove black dust that can cloud your tank. The carbon will remove almost any chemical added to the tank water, so if you must medicate your tank, remove the carbon for the duration of the treatment. You will need to replace the carbon periodically. If the activated carbon does not remove the yellow discoloration, add more, or try using a higher grade of carbon (ask your aquarium supplier).