Are you checking your PH? What is it at?
Is it getting worse? If no then keep up what your doing... if it is then bump up the water changes.... it's never going to totally heal or get better but because it's a small RTC it won't look so bad as it gets bigger... Even Necro's had some Gill Curl if I remember correctly and it's hardly noticable now...
This looks much worse than his case though...