Originally 1 1/2 years ago, I filled with tap water. (Big Mistake, I've since learned)
I purchased an RO
unit last April, and have using that ever since.
I have two Clowns, a scott java damsel, and the starfish. 75 gallon tank.
PH-8.2 Ammonia-0ppm Nitrite-0ppm Nitrate-20ppm
I called my LFS
and the guy said that it is a pond block... :-/