I have now mined a number of coins with Genesis Mining and they have ALL gone the same way - they start off ok and then little by little they reduce until there is hardly any daily payout.
Has this happened to anyone else?
This is called difficulty adjustment. Mining difficulty changes over time. For Bitcoin it has increased for a few month and is now relatively stable.
https://bitcoinwisdom.com/bitcoin/difficultyMy BTC payouts are relatively stable, as well.