Black ghost knife and discus ?

[Rory H]

Hi. I'd really like to breed discus but before I think of buying some, I'd like to know if my bgk will cause problems. He's about four inches long but he's too big for any other tank I have so I need advice. Currently I keep him and about twenty guppies. They're my son's but he's got all enthusiastic having bred Siamese fighters recently
Any one able to help ?
Thanks