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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
Find out what tools you’ll need and discover the best way to get your aquarium back on track without starting over and find out how to maintain a clean fish tank.
Updated on June 12th, 2026
We can help you navigate your way through all the types of lights in fish tanks and determine which type is best for your aquarium.
Updated on June 19th, 2026
Search Petco to learn about blackwater fish aquariums. We want to help you decide what lifestyle is best for your unique fish.
Updated on June 19th, 2026
Before establishing an aquarium at home, learn more about the basics of fish care.
Updated on June 19th, 2026
Check water chemistry first. Use 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 20 ppm or less. Perform partial water changes, no more than 30% at a time, to stabilize chemistry and/or to improve water quality. Use only conditioned water that is temperature matched to prevent stress or shock. Check water temp as well. Any of these can drive a fish to the surface. The "flashing" (darting about) can be due to infection (bacterial, fungal or parasites). Consider a broad spectrum antibiotic or an "all in one" product to treat multiple infections. Look in the Aquarium section of the local Petco for options. Follow label directions carefully and remove the carbon filter insert during treatment if indicated.
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
Thanks for your question about your fish, and congratulations on your new family members! I didn't see how recently the tank was set up, but there are a couple of things that could be going on. I would start by checking your water quality - any abnormalities in water quality can make fish have abnormal behaviors, and the water looks a bit murky in the photos you provided. There may be parameters that need to be addressed depending on what you find. If you do not have a water quality kit, they can be purchased at the pet store or an aquarium store, or you can take a sample of your water in for evaluation to these places as well. Some will charge a small fee for this service, just so you are prepared. Also, with recent tank set ups, it can be stressful for fish as they are in a new habitat. I would recommend keeping the light on for only a few hours per day to start, as the bright lights can be shocking for them (since fish don't have eyelids). Gradually you can increase the length of time that the lights are on so that you reach a cycle of 10-12 hours of light and 12-14 hours of darkness for them. I hope this gives you a place to start, and I wish you and your mom the best with the new pets!
Updated on September 24th, 2025
Those could be copepods. They are typically harmless and difficult to completely eradicate. On the good side, they are a sign of a healthy tank and are useful in eating decaying matter in the aquarium. The brown algae can be due to insufficient lighting or lighting periods. You can wipe down the glass and plants, perform a partial water change and increase lighting. It can take weeks to month to resolve. Use only aged or conditioned water that is temperature matched to prevent stress or shock. Confirm stable water chemistry and quality. Make sure the water temperature is correct as well. Too warm or too cold can cause stress. Look the Jack Dempsey over for signs of injury or infection. Ich, bacterial infection or fungal infection can cause the fish too twitch or shiver. Plain aquarium salt (NOT table salt or Epsom salt) dissolved at 1 tablespoon per 5 gallons of water is a great general tonic that can reduce stress, improve gill function, treat minor infection and aid in any recovery. The eels should be fine, but the snails should be moved temporarily. You can relocate both to a separate tank to be completely safe. Treat the tank for 10-14 days then reassess the condition of the fish. Perform a partial water change afterwards to reduce salinity before you returns the eels and snails to the tank.
Updated on September 24th, 2025
Thanks for reaching out about Fishy. A UV sterilizer will only help if a bacterial component is adding to the cloudiness. More intense water changes are the best way to remove nitrates. Monitor feeding to limit excess, vacuum bottom of tank to remove degrading detritus. Good luck.
Updated on September 24th, 2025