Goldfish are often labeled "dirty fish" in the aquarium trade. While their heavy food intake does equal substantial waste output, regular maintenance can keep your goldfish and their living quarters clean and healthy. Proper gravel-cleaning is key to the overall health and cleanliness of your tank and pets.
The Role of Gravel
Gravel isn't just an aesthetic addition to your tank, it helps keep your water and your fish clean and healthy. Gravel is essential for biological filtration -- it gives the "good bacteria" that break down your fish's waste a place to live. It allows goldfish to satisfy their natural foraging behavior, which involves many hours each day of digging, sucking up rocks and spitting them back out. Gravel should be at least 3 inches deep and small enough that it doesn't pose a choking hazard to your fish.
The most effective means of cleaning goldfish gravel is a gravel vacuum. This is a small siphon attached to a piece of plastic tubing. It's inexpensive and readily available in aquarium and pet stores. You clean the gravel during regular water changes by placing the siphon into the tank and pumping it vigorously until water begins to flow through. As you drain the water into a bucket, use the siphon to stir up the gravel inch by inch until you've vacuumed the entire floor of the tank. It will suck out most of the waste you stir up. Afterward, replace 25 percent to 40 percent of the water during a water change. Frequency depends on your tank's size, method of filtration and number of fish. Bowls with no filter need weekly water changes; tanks with filters need at least monthly ones, sometimes more if they're inhabited by more than a couple of fish. Always treat your new water with a water conditioner that removes chlorine and chloramine before giving it to your fish. Conditioners that include a "slime coat" are best for goldfish.
Some aquarium store workers strongly push the under-gravel filter for "dirty" goldfish with the claim it will keep your gravel clean. Not so. These filters are entirely unnecessary and may even be harmful. They do not remove more particulate matter than a suspended filter and they'll disrupt your biological filtration and live plants. They can also injure your fish as they dig in the gravel. Additionally, under-gravel filters are more difficult to clean and maintain than suspended filters. Canister filters and bio-wheels are better options.
Under normal circumstances, removal of your fish from their tank during water changes and gravel cleaning is never be necessary or advisable. A gravel vacuum should be all you need. However, in extreme cases, such as certain parasite infestations or diseases, you may need to remove all of the gravel and rinse it thoroughly with running tap water if medication alone doesn't work. This will destroy your biological filtration, and your fish will be very vulnerable to poor water quality and infection until the beneficial bacteria re-establish themselves. Never use soap or other cleaning agents on gravel or aquarium furniture. Residue will remain no matter how well you rinse it, and it will ultimately fatally poison your fish.
Normally you want bacteria and other microorganisms in your gravel because they break down fish waste and keep the tank healthy. However, in the event of one extraordinary circumstance, you do need to kill off all of the bacteria and other microorganisms in your gravel. That's when you're dealing with a toxic bloom. These are very rare. They generally occur only in fish tanks when you feed live food in water that's too warm -- over 80 degrees Fahrenheit. You know it's a toxic bloom when the water is completely opaque and it stinks to high heaven, most of your animals are dead, and replacing the water doesn't help. Eliminating a toxic bloom involves removing all animals from the tank, throwing all of your plants away, and soaking the gravel in a 10 percent to 20 percent bleach-in-water solution for up to 12 hours. Then you must thoroughly rinse the gravel and tank under running tap water and soak it with dechlorinator-treated water for up to 12 more hours, preferably with several changes of dechlorinator and water. This method is not recommended, especially for beginners. It's very difficult to remove all of the chlorine, and you run a high risk of accidentally killing your remaining fish.
Angela Libal began writing professionally in 2005. She has published several books, specializing in zoology and animal husbandry. Libal holds a degree in behavioral science: animal science from Moorpark College, a Bachelor of Arts from Sarah Lawrence College and is a graduate student in cryptozoology.