Check spam comments location (which post/page is spammed) and type (simple comment, pingback or trackback). And disable pingback or trackback comments.
I have comment form enabled on all post, page and attachment. Everything was normal I have been getting the spam comment since last few days before I never got a single spam comment when using wpdiscuz so I am kind of surprised.
Ok, then you should check what have you done, what have you updated and what’s new have you installed. You’ve opened new door for spammers and that’s door is not wpDiscuz comment form for sure. It seems spammers have founded other ways to insert comments in your database.
I don’t want to use akismet because I have read a lot of articles of it slowing down the site.
It only works on new comment submission, It doesn’t work on page loading or comment listing processes. Thus it can’t affect your page speed.
Finally you can install other spam protection plugins which are integrated with wpDiscuz:
WordPress Zero Spam
WPBruiser {no-Captcha anti-Spam}