Bettas and Goldfish

Question
how dangerous is it to have a goldfish and a betta in the same tank? Does the presence of a goldfish cause cloudy eye in bettas? Are there any risks? If so, please describe them.

Answer
Bettas, and Goldfish should never be in the same tank for many reasons.
The Betta is a tropical fish, and needs stable heated water of 80-82 degrees.  He is a loner ,and needs a 5 gallon tank all to himself or when kept with tropical fish such as platys, he should be in a cycled 10-20 gallon tank.
A betta needs clean water, and his water should be changed every week in a 5 gallon tank.  Goldfish are messy, and live in alkaline water.  Bettas live in neutral water.  This is very important.
Goldfish, and Bettas should not be in the same tank.
Lynda