Thanks for the definition. I feel better now.

One more question........

If I convert my 220 gallon FOWLR tank to a reef tank, I know I should
have 350 or 400 pounds of LR. I have maybe 25% of that now. But I'm
not so sure about the DSB. Do I put the 4-6 inches in the main tank,
or in a separate tank/sump? If the answer is a separate tank/sump,
what do the dimensions of that tank need to be to handle such a large
tank?

Thanks again for the help.