Just thought I'd share my experience as my perimeter are different. Before I do, by change did you have a low pressure front come through the day they spawned?My tank is a 65 gallon tall, 3f and 4m. Thank Matt's are otto's and a betta. I keep the tank at room temperature, I have to fertilize bi weekly just to have nitrates due to the plants. I run an eheim 2213 & 2217 with a hydor 825 gph power head. I wish I could predict when they spawn but I can't, I just feed them live and frozen food to keep them healthy and nature seems to take care of the rest. On a side note I believe that my group is getting to old for breeding as the spawns lately have been small. Good luck with your group and fry.