Is it harmful to fish??? I have it in my tank and my fish are getting sick one is dead, all were healthily fish had for 2 years, they were treated for parasites around the same time i got the new gravel.
It's more likely it was the parasite treatment than the gravel. I'm assuming the fish had some sort of parasite since you treated them, so that also could have caused the death. What kind of parasite do they have? Another possibility is that you could have put them into shock when you put in the new gravel. Did you take all the water out of the tank when you put in the gravel? If so, the fish may have went into shock from a temperature change if you took them out and then put them back into new water. If you changed all the water, your tank also has started they cycling process again and they may be suffering from ammonia poisoning. If you will add some more details on exactly what you did and why, I will check back on the question later and try to help you figure out exactly what's going wrong here, or feel free to email me :-) I'm always here to help
