Goldfish Aggressiveness?

[EmericaJT]

I've kept 4 goldfish for a about 2 years. One of them is a big one(7 inches) and the others are small (3 inches). They are living together in a 100 gallon aquarium with a Fluval 405 Filter running. A month ago, I bought another red and white common goldfish that's also about the same size as the 7 inch goldfish I have at home and the old and new goldfish don't get along well. The old one and seems to bully the new one along with the other small goldfish. Is this goldfish aggression? I thought all of the same variety go along okay. I guess not. I did some research and they said I should get a tank divider called "egg crate" which was actually called a light diffuser. I bought one and shaped it to fit in my tank. I divided half the tank separating the new one by itself. It has been like this until this morning, I decided to take out all the old fish and leave the red and white one in the tank by itself. All the old fish were in a plastic bag full of tank water. After an hour passed, I got the bag of fish back into the tank and left it floating. Then I released them back in to see if anything changes. By doing research, this was also an option to get the goldfish to feel new to an aquarium. But at the end of the day, they went back to chasing the red and white goldfish. I don't know how to fix this! I know this isn't mating because the old goldfish is nipping at the new one's fins and scales. Now she is really stressed and lying on the bottom of the tank. The new fish is the innocent one, I don't know what is up with the old goldfish. They're really mean!
Youtube Video of my Goldfish:
100g Goldfish Tank - YouTube

 

[Coursair]

I've kept 4 goldfish for a about 2 years. One of them is a big one(7 inches) and the others are small (3 inches). They are living together in a 100 gallon aquarium with a Fluval 405 Filter running. A month ago, I bought another red and white common goldfish that's also about the same size as the 7 inch goldfish I have at home and the old and new goldfish don't get along well. The old one and seems to bully the new one along with the other small goldfish. Is this goldfish aggression? I thought all of the same variety go along okay. I guess not. I did some research and they said I should get a tank divider called "egg crate" which was actually called a light diffuser. I bought one and shaped it to fit in my tank. I divided half the tank separating the new one by itself. It has been like this until this morning, I decided to take out all the old fish and leave the red and white one in the tank by itself. All the old fish were in a plastic bag full of tank water. After an hour passed, I got the bag of fish back into the tank and left it floating. Then I released them back in to see if anything changes. By doing research, this was also an option to get the goldfish to feel new to an aquarium. But at the end of the day, they went back to chasing the red and white goldfish. I don't know how to fix this! I know this isn't mating because the old goldfish is nipping at the new one's fins and scales. Now she is really stressed and lying on the bottom of the tank. The new fish is the innocent one, I don't know what is up with the old goldfish. They're really mean! Youtube Video of my Goldfish: 100g Goldfish Tank - YouTube

Sorry to say, Too many fish. I know your tank looks big enough. Id rehome both larger fish to a pond and later move smaller fish out as well. 3 Fancies could live in 100g their whole life. Not Common or Comets. Make sure you keep testing your water also !

Buy Prime water conditioner if you don't already own some. Buy a master Test Kit. Test your water before and after the water changes.

Goldfish get BIG, they poop a LOT and they can live a LONG TIME with good care and proper sized environment.

Fancies can live 15+years and get over 6" body length without tail
Comets can live over 25 years and get 10-12" or larger.

The record for age is 43 years
The record for length is 18.9"

You have no visual barriers or hiding places. 5 Goldfish is very overstocked I know it doesn't look that way. Your small ones aren't growing as fast, that is a major clue. Your fish look healthy, that's great. You obviously have taken good care of them. But they need even more room to grow and thrive.
Buy a big plastic bin if you need temporary quarters for the new fish. Give him a rest. Find him a pond.

 

[Coursair]

Oh and Id post this thread elsewhere so more people see it. Regional forums isn't the best for fish questions.

 

[Babakapusta]

Chasing is one thing, actual fighting is another. They are probably going through a getting to know you stage. They also are probably setting up who is the alpha fish. Unless your fish look stressed maybe you should just watch them for a day or two to see how far they go. You tank is very bare. You have no place for the fish to go to hide. I think that may be a problem as well. You could buy some slate and make a few caves for them to hide in or behind.

 

[jlk]

Aggression is goldfish is a lot more common than people may realize. The biggest factor in this is a simple one- lack of sufficient space. Five decent sized commons in a 100g tank is simply too many. If you placed these five in a 1000g pond, you would likely never see any aggression (except for breeding but that's a different story). I would give serious consideration to rehoming most of these guys to a happy pond as this will only continue until something untold occurs.