How many fish can I safely and properly put in a 30-gallon tank?

Thanks for reaching out, the rule of thumb is 1" of fish per 3 gallons, but smaller tanks are very difficult to keep stable, and saltwater fish are easily stressed by environmental fluctuations (salinity, temperature, dissolved oxygen). Good luck.

Thanks for reaching out about your fish. Typically, most recommendations are 1" of fish per 3 liters of water. The better the filter system, the better the water quality and the more biomass can be handled. Remember, fish grow and therefore the biomass will increase. Good luck.

Adding more fish would likely cause overcrowding. This, in turn, could lead to stress, illness and aggression. You are probably at or very close to maximum capacity, especially if you have fish that are still growing.

Hi there! The general rule of thumb is 1 gallon for each inch of fish, so I think that you may need a bigger tank. If the bettas are 2 inches each, they each require 2 gallons of water, making the minimum tank size 14 gallons. Since male bettas can be territorial and aggressive, I highly recommend a larger than normal tank with lots of hiding places for 7 fish (at least 20-25 gallons). You should also watch them very carefully for fighting, and have a backup plan in case any of them need to be separated. Good luck!

The goldfish can get very big and may require a significantly larger tank as they grow and grow. As a rule of thumb, you need 1 gallon of water per inch of body length of fish. So if you have three 1 inch fish, you will need 3 gallons of water. I suspect you are at your max already in the smaller tank. Just so you know, most people do not have goldfish in tanks with tropical fish. You may consider getting two tanks One for your cold water fish like the goldfish, and one for your tropical fish that require a warm water temperature. For the goldfish I would suggest a minimum of a 20 gallon tank. For the Danio, I suggest to get a few more of these as they are schooling fish and a 10 gallon would be just fine. I hope this is helpful and please feel free to post any additional questions.

All these fish can grow quite large. The loach would be the "smallest" at about 6 to 8 inches when full grown. The Oscars can reach lengths of 18 inches and the Texas cichlid and sharks can reach a foot in length. All these fish will require much larger tanks than the ones you have now. The three Oscars alone would do best in a 125 gallon aquarium MINIMUM. The others may thrive in 55 to 75 gallon tanks. To leave them in small tanks will cause stress, aggression and likely infection.

In general these fish can all be housed together safely. The one thing to keep in mind is the amount of space needed per fish to maintain a safe and healthy environment. Each 1in of fish needs 1 gallon of water. So in a 20 gallon tan you can have 20 inches of fish. The Pleco is the only one I have concerns with as some varieties can grow quite large. Check with your local pet shop as to what needs best suit this type of fish or what type of fish suit your tank best.