those posts really surprized me.

that sand was not only NOT a good idea for
goldfish in the tank but also was not good for them at all? It was stated
thast the sand Irritated the gills?

I don't know who invented the gill irritation story but I know it's conjecture
at best.
Every pond in the world gets dirt in it and the result is multi sized grains of
"sand" on the bottom.
Fish gills are a marvel dealing with the elements found suspended in water.
I can say that the finer the sand, the better the bottom stays clean and
watching my fish forage in it, they suck up lots of sand and blow it out. Never
a problem, after many years of sand.