They do increase as you post more. I'm not sure exactly how many it takes to get to each level though. Keep in mind when you are looking at posts and replies to problems you may have that a member having a high post count doesn't necessarily mean they are an expert on fishkeeping. There are some members that just joined in September and have only had fish for 3 or 4 months but have 1500 or more posts and other members who have been members for 2 or 3 years and have 10 years experience in fishkeeping but only have 300 or 400 posts. So post count and knowledge are not related at all.