I don't know what's going on the past few years. Growing up, and all the years I've been married and preparing and going to seders, the freshly grated horseradish was nice and strong, just like maror is supposed to be. Children cried because they were afraid to try it. My brother-in-law's father almost had a heart attack showing off how he could eat a big spoonful at once. All was right with the world and just as it should be.
For the last few years, though, it's certainly strong enough when freshly grated, but a couple of hours later at the seder it has lost all its heat. I'm careful to cover it with plastic so there's no air on the surface, but no matter what I do it's not even recognizable as maror. This year we reorted to cutting it into little chunks, which were strong. But the same horseradish grated - - - nothing.