Gary Dawg wrote ...

Can't imagine how bad
it would be in a month, never mind a year.

Not bad at all. In fact, if you have a glass-bottomed tank on an open-top
stand you can look and see. I have a tank that's been up, I think, seven
years and there is a whole 'nother happy, healthy ecosystem going on under
the filter plates. Remember, the nitrifying bacteria are breaking down all
that mulm and shipping it back up the risers into the water column to feed
our plants.

You can definitely keep your gravel squeaky clean and that works, too, but
you're throwing away valuable fertilizer. Besides, I don't like working
that hard.