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Discover the fish tank filter system that’s right for your aquarium. Learn about mechanical, chemical, and biological filtration at Petco.
Updated on June 19th, 2026

One of the oldest forms of aquarium filtration (and not just for small tanks), a sponge filter may be the right filtration choice for your aquarium!
Updated on June 19th, 2026
Gravel vacuuming helps remove solid waste from your substrate. Learn about the different types of gravel vacuums available & how to clean your fish tank.
Updated on June 19th, 2026
Discover how to hardscape your aquarium here at Petco. Visit Petco and check out aquarium hardscape ideas, solutions and much more for your fish.
Updated on July 17th, 2026
Learn how to care for semi-aggressive fish, recommended diet & aquarium setup. Find the right food, supplies & equipment at your neighborhood Petco.
Updated on April 9th, 2026
Some iron is necessary for a healthy aquarium, but too much can promote algae growth or impart an unsightly yellow or orange tinge to the water. Reverse osmosis (RO) filters are deal for removing mineral and heavy metals from water but they can be prohibitively expensive. Buying RO water from a local market or pet store is also a possibility but not economically feasible if you have a large tank. The best option may be a Polyfilter, which can be purchased in the local pet store or online. These filters will remove iron or other metals/chemicals and must be changed monthly or quarterly. You can also buy a water conditioner that will precipitate out some of the iron which can then be removed by mechanical filtration. An example of just one is Rid Metals (by Kordon). Follow label directions carefully, perform regular water changes and monitor iron levels with a home test kit or by submitting a water sample for testing.
Updated on September 24th, 2025
Check the water chemistry using a home test kit or submit a water sample for testing. The local Petco may do this for free or for a small fee. Aim for an absence (0 ppm) of ammonia and nitrites with nitrates at 20ppm or less. Perform partial water changes to stabilize chemistry and/or to improve water quality. Rinse the filter media in tank water, not tap water, and replace it. Use only conditioned water that is temperature matched to prevent stress or shock. To limit algae growth, maintain pristine water quality via filtration and regular water changes. If possible, turn up filter flow to keep water moving. If this stresses the fish though, do not do it. Do not overfeed and remove any uneaten food promptly. Limit lighting to 8 hours daily and closely monitor water temperature as well. All these can promote algae overgrowth.
Updated on September 24th, 2025
It is possible the tank has not cycled properly which results in high ammonia and nitrite levels which can kill fish. Allow the tank to run, without fish, for at least 4-6 weeks. During this time, use a home test kit or submit a water sample for testing every few days. The local Petco may do this for free or for a small fee. What you are looking for is to have ammonia and nitrites at 0 ppm and nitrates at 20ppm or less. pH can hover around 7 for most community fish. Avoid large, rapid swings in pH though. What is happening in the tank during this time is that beneficial bacteria are populating the gravel/substrate and the filter. These bacterial populations are responsible for the Nitrogen Cycle. This cycle breaks down wastes from fish, uneaten food and plant matter into by-products that are filtered out or dissipate. You can "cycle" a tank with fish, however this increases the risk of loss. Once your tank has cycled, you can add fish. You will still need to monitor water chemistry and perform partial water changes regularly. Use only conditioned water that is temperature matched to prevent stress or shock. You will also need to vacuum the gravel regularly and rinse the filter media. Never use tap water to rinse. Use a bit of tank water to protect bacterial populations in the sponge.
Updated on September 24th, 2025
I'm sorry you are having difficulties with your aquarium. There are several issues that should be dealt with right now. They are water chemistry, aquarium size and choice/number of fish. Any new aquarium should be set up and, ideally, run empty for several weeks (usually 4-6 weeks). This is so beneficial bacteria have an opportunity to populate the substrate and filter. These bacteria are necessary to break down wastes that fish will produce. The technical phrase for this is "establishing the Nitrogen cycle". These bacteria will break down wastes into ammonia then nitrites then nitrates. Nitrates can then dissipate or be absorbed/used by live plants. In high enough concentrations, ammonia and nitrites are toxic and can kill fish. Cycling a tank with fish is possible but it increases the risk of loss. Water chemistry should be checked every few days using a liquid home test kit. A water sample can be submitted for testing , but is not as convenient as testing yourself. Most pet stores or fish stores will do this for free or for a small fee. Partial water changes, no more than 30%, can be done as needed to stabilize chemistry and maintain water quality. Choices for water conditioners include NovAqua, AmQuel Plus, Prime, StressZyme or StressCoat. Tank size is another concern. With most fish, the widely accepted "one inch of fish per gallon" will be sufficient. For koi and other carp species, including goldfish, the rule is not sufficient. At full size, goldfish need 20 gallons per fish with an additional 10 gallons for each additional fish. Koi do best in larger tanks, much larger...we're talking in the hundreds of gallons or small ponds. These species produce a larger than average bio-load (wastes) that can quickly affect water quality in a tank. To combat this, large water volumes and powerful filtration are required. Any filter should be rated for at least twice the tank volume. I'm not sure what size tank you have now, it may be fine if the fish are young and small, but they will quickly outgrow it. The last issue is choice of fish. Koi and goldfish are cold water fish. They do best in water between 65F and 72F. Most species of sharks do best in the high 70sF to low 80sF. Keeping fish in incorrect water temperatures will lead to stress and illness. This could be compounded by the water quality/chemistry issues you are having currently. Until the chemistry is stable and water quality is maintained, your fish will continue to become ill and possibly die. Any treatment will not be successful in this situation. Do not purchase or add any more fish until the tank has cycled. If you have additional questions, you can post them in the forum or request a consultation to discuss the case in greater depth.
Updated on September 24th, 2025
RO water is devoid of minerals and trace elements that help stabilize pH and other parameters. If you can add these after filtration then use your RO water. Otherwise, RO is commonly used to "top off" fish tanks that lose water via evaporation.
Updated on September 24th, 2025