I have a 20 gallon without fish that is cycling. I accidentally dropped a sponge in there. The sponges have chemicals on them. Would it be safe to put fish in there,or should I clean it. Would it be safe even if you clean it?( The sponge is the kind you wash dishes with.)
How did you drop it in? Did the sponge have a dishwashing liquid in it? If it did, there is a good chance the dishwashing liquid killed the beneficial bacteria in your filter. If you have no fish in it, you could clean the tank and put new filter media in the filter, and cycle the tank anew. I personally would be afraid to put fish in a tank that had dishwashing liquid in it.
But this sponge WAS previously used for washing the dishes, correct? If so ... I don't really know because there surely are at least trace amounts of the dishwashing liquid in it. Maybe you should wait for some other opinions. As for myself, I personally would not put fish into the tank in which there was a sponge that is used for dishwashing.
Well then, if it was a brand new sponge, never used for anything (no chemicals ever were in contact with it), maybe your tank water is safe. I really can't tell because I don't know if this sponge wasn't chemically cleaned in the process of making it (before you ever bought it). I'd really ask Carol (Butterfly), Gunnie, or Rose (Chickadee) about it. If you have a test kit (tests for ammonia, nitrite, and nitrate) you should test the water to see if it's continuing to cycle. If it is, that means there are the beneficial bacteria, and that they were not killed by whatever the chemicals the sponge might have had. BUT there are many chemicals in the water for which there are no tests and that should be removed with regular water changes. So as I've said, get a second opinion just to be sure what to do.