Why did my corys stop laying eggs?

[Nina]

I have four albino cores in a planted, established 20 gallon with some tetras and rasboras. I've had them about 1.5 years. They use to lay a TON on eggs -- if I fed them a lot I'd see eggs on the glass at least once a week, sometimes several times a week. Over the past 3-4 months they've stopped and I haven't seen ANY eggs. 

What could be going on? The only thing I can think of that has changed is the season -- they stopped in late fall. I have a light, but they do get some ambient light from a window.

Could there be something I'm missing? My parameters have been pretty stable but I haven't been monitoring PH a ton in that tank because it has crushed coral and usually seems to be in the 7-8 range. 

What makes corys unhappy? 

[TheSwissAquarist]

Try feeding more livefoods, that normally induces spawning within a couple of days. A short temp drop can also work magic.