Actually, Watermom, many filter instructions call for gravel up to an inch or two above the laterals. Having it there improves water distribution. But gravel can be in the filter sand, because the gravel at the bottom got mixed with the sand on the top . . . or it can be because it was crummy ungraded sand.
If you find that there is mostly gravel at the bottom, you can just put that back in.
Either way, make sure that water covers your laterals, to reduce the impact when you start pouring sand or gravel back in.
Ben
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