My site is growing up with many new visitors and alexa says that my site is going down.Also alexa don't get new fresh content from my site,has the same content indexed that 3 years ago.
alexa decrease only in case your visitors use alexa toolbar each time they visit your site if they dont use then no alexa decrease at all
i have more than 10 wbsites,one of them have just 700 visits,thats alexa rank is 108.950 and the other have 1500 and more visits thats rank is 322,609,that is alexa... a funny program and cheating service,avoid alexa rank,that is better