Coral is freshwater aquarium causes cloudy, deadly water?

Question

A friend did this because the store did not tell him he couldn't and after two weeks you could hardly see the fish, half died and finally someone with half a brain at one of the pet stores asked what all was in the tank. Coral was a big no no, only for salt water tanks. Looked good but deadly

Answer 1

Oh my god. That is probably one of the worst things to do to the coral. Most of it is actually alive and without the salt in the water the coral will die. It probably put some kind of chemical in your freshwater tank killing the freshwater fish and without the proper chemicals, it killed your coral. Big, HUGE, no no. Sorry to be so harsh but that was a little stupid. I wouldnt at all suggest you, or anyone else, do it again.

Answer 2

I would agree. Crushed coral (or aragonite shell) can be used as substrate in freshwater tanks, but in only a few instances. The material that makes up these is aragonite, which is mostly calcium carbonate (CaCO3). It dissolves in mild acidic conditions and will raise the pH of your water to levels in the high 7s (at least) to around 8.2, giving off calcium which will raise your water hardness. So you need to have fish that like high pH and high hardness to use this - mostly fish in the cichlid family.

Crushed coral and shells also carry a lot of dust, which can make your tank even cloudier - it's almost impossible to remive the dust completely by rinsing the substrate first.

As for living coral - saltwater tanks only!

Answer 3

This would depend on the type of freshwater fish he had (assuming this is DEAD coral).
If this was live coral NO WAY!

As for dead coral (coral skeletons used as decor):
Coral is loaded with Calcium Carbonate, with lesser amounts of:
sodium, magnesium, strontium, potassium salts of carbonate, bicarbonate, chloride, sulfate, borate and MANY other trace elements.

This can actually be beneficial to Rift Lake African Cichlids, however this will also elevate the GH and KH of say a Tetra tank to undesirable levels.

I would recommend testing ALL parameters just to make sure something else was not wrong as well, this would include:
*Ammonia (0)
*Nitrites (0)
*KH (80 is fine for most general FW)
*GH (80 is fine for most general FW)
*pH (this depends on the fish in his aquarium)
The proper KH and GH also varies with fish type.

Make sure and have him change 50% of his water as a precaution as well.

I would suggest reading this article about KH, Calcium and Electrolytes:
http://www.americanaquariumproducts.com/AquariumKH.html

Or ths article about basic freshwater care:
http://www.americanaquariumproducts.com/Basic_Aquarium_Principles.html

Tell him not to give up!