do you guys know how a pool works?
variance in your effective hashrate is caused by the pool calculating your rate based on the number of shares you submit in a given period
If you're lucky you'll submit an above average number of shares and the pool will show your effective rate as being higher than usual. so if you're unlucky and submit fewer shares in a period then your effective hashrate will drop below the hashrate that you're actually mining at
over short periods of time this can result in large variations
If you look at your average hashrate over a longer period (=you mine constantly during that time) then it should be close to your actual rate.