I have notice from few days my website index rate suddenly going down. my site contain 2.5 million pages and i have set Google crawl rate maximum in webmaster tool after it Google index my pages continuously when it reach around 13 lac suddenly Google index rate going down and day to day it show decreasing now present it show 12 lac's only. in between it was reset Google crawling rate. and Google show 90 days period for indexing all pages.

i don't know what happen in Google indexing please guide or any suggestion for it.