It is going to fluctuate depending on the share rate that the pool has relative to the Net hashrate of the coin.  If more miners flood into the coin your relative hashrate and therefore share is reduced and therefore your payout is going to be less.   This is why you can't effectively mine Bitcoin directly unless you have a massive hashrate because the net hashrate of everyone in the world is massive.  It also may be that miners are shifting from one DGB algorithm to another affecting the difficulty and share of one vs another.  To maximize profits you'd have to compare your hashrate for the algorithm compared to the overall difficulty/net hashrate of the algorithm and even then if there are more miners coming to mine the coin you'll end up with less returns.  Also if the overall hashrate of the pool increases your share of all the coins found by the pool will be less as well.