No, the only time I change out the substrate is if I decide I want to start all over, and then it's usually just for aesthetic reasons or decide I just want to try something different. (I'm breaking down my 10gal with Red Fluorite to replace it with black Flourite, for example).
Substrates will lose nutrient content over time but that's easily supplemented with fert tabs and/or ferts in the water column. It shouldn't ever be necessary to change a substrate.
2-3" total of substrate is usually plenty for most plants. I have 4-5" in areas of my 90gal but that's just b/c I want to grow some large swords, and they put out some massive root systems.
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