This here is a list that a few of us compiled of fish that should be avoided unless you are an experienced keeper and have the tank space.

1) The Pacu- This thing can get huge i mean huge. You need at least a 2000g tank to house this. They get up to 30 inches.

2) Iridescent Shark- These things get huge too! Just look them up on google and see what you find. They can get up to 4 ft.

3) The Red Tail Catfish- Another Monster catfish. They can get up to 4 feet in length. There is a two other kinds of them out there, Red Tail Catfish mated with a Shovel nose catfish which get larger and the Asian Red tail cat which get big to.

4) The Common pleco- This is one of the most misunderstood fish. These fish get very large and put off high bioload. Some have also been reported to suck of the slime of your fish. They can get up to 1-2 feet and should be kept in aquariums larger then 100 gallons.

5) Arowana- There are many different types of Arows. such as silvers, jardines, black, super reds and so on. The most common is the silver and they get big. They Get somewhere around 3-4 feet and a tank 2 times there size and need to be able to turn around.

6) Hi Fin Banded Loach- Some of you might not see this kind of fish at some might see it a lot. They get pretty large buts thats not the problem. They like cold water and don't do the best in tropical water. They also get aroudn 1-2 feet and like to shoal of at least 6 to keep them happy.

7) Bala Shark- These are really common too! They are a cool looking fish and may be sold under the name silver shark. They get big too! They get around a foot long and need to school. They need 350 and at least 6 to school with to be happy.

8) Tinfoil Barb- They have around the same standards as the Bala Shark.

9) Black tip Sharks catfish- They are sold as brackish and get 12 inches and need full marine tank when full grown. They also like to school.

10) A.gigas- The biggest freshwater fish in the aquarium trade. Enough said.

11) Any type of Sturgeon- They get huge almost as big as the fish above. They also need cold water and fast current.

These are some fish that need a bigger home then most of the beg. or even me can provide. I would do proper research before anyone should by these fish or any fish at that.
Thanks for everyone who helped me make this list :)