coral in a freshwater fish tank.......

Question
05 May, 2007
I have a new 16 gallon bow front tank set up & functional since 01 May,2007. Mardel Aquarium Starter Test Strips read 0 chlorine, 0-0.5 nitrate, 120 ppm hardness, pH 7.6. Water Temp 80 degrees with all live plants and bubbles.
Added this late evening were 6) zebra danio & 1) red fire dwarf gourami, doing wonderful.  Filter system is Penquin Biowheel 200 & air bubbles added.  My Question is in the aquarium 3 separate coral pieces are placed, would they be harmful to my fish now or in future? They are (of course) not live and boiled the daylights out of them. Now that I have blah blah blah...I will bid you good evening.  
Awaiting your reply, best regards,
Lady Martha  

Answer
Hello Lady Martha;

Coral and shells are not good to use as decorations in freshwater tanks. Corals and seashells are the skeletons of dead animals. Skeletons are made of minerals and those minerals and will never stop leaching into the water. They harden the tank water and raise the pH over a period of time. It's fine to raise hardness in saltwater tanks but most freshwater fish can't tolerate it that high. Your weekly 25% water changes that come from your tap are likely to be drastically softer too so they could be stressed. Unless you were to coat the coral pieces in thick epoxy or something similar that is safe for your fish when cured, there is nothing you can do to prevent it from happening.  

You have quite a few fish in there for such a new tank so I will "stick my nose" in here to give you some help with it. I'm a little worried. Monitor ammonia and nitrItes. (Not nitrAtes, it's different and far less toxic) I didn't see them on the list of results. Below is a link to my web page about "New Tank Syndrome". You will hopefully find it useful as your tank goes through the break-in period in the coming 6 weeks;

http://www.xanga.com/Expert_Fish_Help

I hope all goes well...

At Your Service;
Chris Robbins