We mine LTC in clevermining.com pool. Day by day LTC payouts are getting lower and lower, though total hashrate is not changing significally. What might be the cause?
Here's the payout chart: https://www.clevermining.com/scrypt/profits
If the total hashrate is staying the same, you should expect your payouts in LTC to stay about the same. But the chart you linked shows payout values in BTC, presumably based on a market rate conversion from LTC to BTC. And as you can see in this chart, the LTC/BTC exchange rate has been falling over the relevant time period. (Note the scale on that chart is deceptive, since the bottom of the chart is not 0.)