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Related Articles & Questions
- Care Sheets
Aquatic Pet Safety: Keep Your Home Aquarium Pets Healthy & Safe
Learn how to safely handle your aquatic life to avoid toxin & bacterial exposure. Find aquatic life care supplies at your neighborhood Petco pet care center.
Updated on October 23rd, 2025
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Best Fish for Beginners: Top Freshwater Picks
Some fish species generally do well in smaller aquariums, are more adapted to aquarium life, & can be slightly more forgiving with water quality fluctuations.
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Marine Shrimp Care for Beginners: Tank Setup, Food, & Compatibility
Learn how to care for Marine Shrimp, recommended diet & aquarium setup. Find the right food, supplies & equipment at your neighborhood Petco.
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Damselfish Care: Expert Tips for a Thriving, Healthy Fish Tank
Learn how to care for a Damselfish, recommended diet and aquarium setup. Find Damselfish for sale, supplies and equipment at your neighborhood Petco.
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- Vet Q & A
Why are my fish dying with bleeding, white spots, and polluted water?
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
- Health & Wellness
Just got a small fish. What breed is it and how do I care for it?
Thanks for reaching out about you fish. It is believed to be a Comet goldfish. Water quality and nutrition is the key to success. Testing water parameter for pH, ammonia, nitrite and nitrate will give you guidance for a healthy environment. Purchased food should be rotated out every 3 months as vitamin C and other nutrients degrade over time. Trying to maintain water temperature can be challenging with out a heater, but most fresh water fish tolerate some changes. Good luck.
Updated on September 24th, 2025
- Training & Behavior
My fish jumped out of tank and bled. What else can I do to help?
Hi, I’m glad Maxi made it through that ordeal! It sounds like you acted promptly and appropriately. Salt and stress coat are the perfect first step, short of an exam by a veterinarian. Since she’s acting normally, I would keep a close eye on her activity, body symmetry, and appetite. If in doubt, or you notice any changes in her regular patterns or attitude, don’t hesitate to take her to your vet. Good job acting so fast to save her!
Updated on September 24th, 2025
- Health & Wellness
Why is my fish sick, not eating, gasping, and darting in its tank?
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
- Vet Q & A
Why do my fish keep dying in my newly set up aquarium?
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
