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Freshwater Aquarium/Plethora of questions



I have a common feeder goldfish that I've had for 2 years, and he's about 4 inches long. He's currently the only fish in my tank, which is a 10 gallon. Last fall, when I realized just how big he was getting, I arranged to have him go down to my grandmother's pond in the spring. After missed attempt after missed attempt, I finally decided to just give up and keep him. I'm wanting to upgrade his tank, which leads me to several questions.

1) I have a 40 gallon breeder tank with the hood, or a 20 gallon breeder with a screen top, that I can use the light canopy from the 10 or 40 gallon over. Which would be the better choice? I don't want to overwhelm him, but I also don't want to switch tanks again in a year.

2) Since I'm upgrading, I'm going to need substrate. At the moment, he's with gravel, and plays with it CONSTANTLY! I'm tempted to switch to sand, but will that hurt him, the way he digs and roots? Should I stick with gravel?

3) He's in a heated aquarium (I know, goldfish are okay in unheated, but in the winter our house gets down to 60*, and up to 90* in the summer, so a heater just seemed the best bet to keep it a more stable temperature). I'm considering adding some more fish, to keep him company and keep the tank from looking so bare. What are some choices that won't pester him/he won't pester? (I'd love to have another cory cat, but I'm not sure if that's a bad idea with a goldfish?) OR should I just leave him alone?

4) I'm seeing mixed results on planting an aquarium with goldfish... some fish seem to uproot the plants, others leave them alone. Is there any way to tell with a goldfish, or do I just put the plants in and hope for the best?

Thank you so much for your time, and I really appreciate it.


It is great that you are so caring for your fish!

For goldfish, the bigger the tank the better. Common goldfish need 55+ gallons, because they grow up to a foot in length. However, I do not know if your fish will grow so large. If a fish is kept in a small environment, it is possible for their growth to be stunted.

If you plan on continuing to keep goldfish, I would do the following:

- Use the 40 gallon and add plenty of filtration -- the bigger the better for goldies. He will be fine in a larger tank, I have found they love to swim back and forth!

- Don't worry about trying to heat it, unless you just really want to.

- Add 1 or 2 "fancy" goldfish. Goldfish really only need to be housed with just other goldfish. Common single-tails and fancy varieties tend to get along fine. You just have to be sure they all get enough to eat because fancies are slower swimmers. You can keep 3 fancies maximum in a 40 gallon.

- Sand is absolutely wonderful as substrate. I have started using sand in most of my aquariums -- waste floats on top, so you don't have to dig around in the gravel. It also removes the risk of the goldfish choking on gravel, which happens a lot, unfortunately. Also, it's a lot prettier than gravel! You just need to take extra care in setting it up and stir it gently during the water changes to prevent dangerous gas pockets from building up. If you have any more questions about sand, let me know and I will be glad to help.

- Go ahead and try some plants. Some goldfish will dig them up, but some won't. It does not hurt to try. You might want to look into floating plants, as well. They couldn't rip them out of the substrate, since they stay on top of the tank, but they would still help control the waste levels.

Even though you cannot put a ton of goldfish in a 40 gallon aquarium, it still has the potential to be a beautiful goldfish tank. The right decorations can accentuate the beauty of the goldfish, and make your aquarium very unique.

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Elizabeth Turbyfill


I am available to answer any questions regarding Betta fish and goldfish. I will be able to answer questions ranging from basic husbandry to health issues and more. I have a fair amount of knowledge regarding keeping freshwater fish in general as well, excluding cichlids. If you have any questions about species compatibility, maintenance, health issues, et cetera I can help. If there is a question that I do not know the answer to, I will look to reliable resources to find the answer.


I have kept numerous Betta fish and freshwater aquariums for several years, and have spent countless time researching them.

I am a member of a fish forum named Tropical Fish Keeping that I highly recommend to people who keep aquariums or just have complex questions that cannot be answered here.

I am currently attending East Tennessee State University for a bachelor's degree in Computer and Information Science.

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