Oh, Im sorry I havent replyed this, thank You all. Well, I bought the fert and used it as freezed with water. It worked oh-so-well and caused no harms at all. I didnt get long time experince with it since I sold the aquarium and havent used that fert since that. Now I do use fertsticks for room plants, inc. ammonium, they work just fine as well.
Urea is urine, ammonium is a "type" on N (as nitrate and nitrite are too), urea contains ammonium as a source of N.