Coral makes water more alkaline. Not good in fresh water.Sorta, just today. And all I had to do was move the love seat , 3 marble tables, scrub w/ vinegar the tank , wash all the gravel find a piece of coral I have had for 20 yrs and rinse it then second think myself if it should be used or not and now I have a dry ugly empty dirty fish tank in a spot I didnt want it to be in the first place with no money for fish or a heater. So, ya. I got started.