Just some of my crazy thoughts:
Value of BTC dropped, which has an effect. But that is only part of the truth. I was busy trading Megacoin (are there other coins
), and while Bitcoin was dropping in dollar value like mad, Megacoin was gaining in Bitcoin value. So, in theory, if the most profitable coin for that day had been set to Megacoin, payouts in BTC should have gone up. Seems logical, right?! So, why didn't GM point their hashrate towards Megacoin?! Because there's more things to consider.
One such thing, if you have 10TH/s of Scrypt power and you point it all at Megacoin, difficulty would go bonkers! Kimoto Gravity Well would kick in on universal level and end the coin harvesting festival completely within one or two blocks. You will waste tons of energy on KGW instead of mining. Byebye profit. And suppose you would get a load of coins, where to go with them and who would buy that many?! You'd dump them on the market and brutally murder the price. Byebye profit.
You would have to consider this when mining the most profitable coin. and this is just one aspect. The whole concept of "mining the most profitable coin" is an incredible puzzle, with a thousand pieces, and only a few minutes to figure out which next piece should go where. That details of course are kept secret, and those that find out will be killed in their sleep.
Also, and this is rather important, I'm saying Megacoin here, but really, picture almost any other coin here. THIS is the real issue of coin value. There are so many of them that buying power is scattered all over the place and none have true buying power supporting them. This means that the most profitable coin is more or less a ghost. As soon as you've found it... it vanishes into thin air again due to selling pressure with virtually no buying support. Nearly all coins are push-overs. Point a finger at them and they cave in. The more coins there will be, the worse this will get. Any coin about to rise above others will be swamped, and killed almost instantly, by sellers. So... the margins for the most profitable coin are rather thin. Take small steps only...
How to fix? Well, improve the whole coin choosing concept, or stick to truly powerful coins only, or add ALL available coins to the pool so you have more to choose from. Or...
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Unfortunately I'm tired and too slow. More later. or not. But someone else may step in also and share a few thoughts of the how and why