doing by parts
I've read that you ought to do a good cleaning in parts, 1/3 or 1/4 at a time. Pull the plants, gravel vac and replant. I never did that but after 5 years the entire tank was declining, the red wentii crypts were almost gone. Yes, I'd slacked on the ferts as well but when I did add ferts it seemed to do no good and my fish slowly died off one by one. So, maybe letting it go that long was a mistake.
I recently did a full tank teardown, took the gravel to the yard to rinse and replanted, restocked. Hopefully I will remember to to a partial cleaning from time to time.