Welcome to the forum!!
I would just keep up with the water changes until nitrites disappear, although 75% may be a bit too much. Good for discus, bad for bacteria colony. Adding additional bottled bacteria won't speed up the process. Now if you see an ammonia spike then keep a close eye on everything and adjust water changes as needed. If you see a larger nitrite spike then adding 2 tablespoons of salt per 10g will help them deal wit nitrite poisoning. I'd guess you have another 2-4 weeks to go.