I have a biorb running with plenty of plants to hide in and stocked with very small fish, neon tetra's, red line tetra's, harlequin rasboras, all about the same size and up until recently male guppies. Who is eating who? The stock levels are gradually reducing with no evidence of the fish that have vanished, all but one of the fancy male guppies have gone, the only one left is very plain with a small non-fancy tail (may even be female) Each of the species have deminished and I've never seen any signs of agression and they were all bought in groups of 6 so they could shoal. The eating happens over night.
The tank is completely cycled and has been up and running for over a year, Ammonia 0, Nitrite 0, Nitrate less than 20 and it has a 10% water change each week and there were no signs of the missing fish when I stripped it down to clean in filter last week.
So my big question is which type of fish is eating the others?