Rice became slimy after refrigeration

I tried cooking black rice and quinoa mix from a store-bought bag and it was good and fluffy the same day, but became slimy and sticky after refrigerating it overnight. It should be a simple problem that has a simple solution. I just need to know the trick. I have the same problem with Jasmine rice. Some people suggested soaking the grain in water before the cooking, which I tried but it didn't help.<br><br>Is it a water-to-rice ratio problem? Do I need to add oil or fat? What's the best rice cooking method? I'm getting close to throwing the cheap rice in the garbage and spending the extra money to buy the Japanese short grain rice. I'm the only one eating the rice so it's not a full bag I'm feeding to a large family.