HI everyone. I'm new to the forum, intermediate in my experience, and looking for some friendly advice on my setup. I have just recently renewed my hobby after a 5 year absence and my aquarium has been occupied for 5 weeks now with 7 zebra danios. No casualties yet and all seem to be thriving. It is a 60 gallon tank, not planted as of yet, at 79 degrees, with a 350 gallon per hour filter hanging on the back that is equipped with two nice, fat 5 inch biowheels. Ph is stable at around 7.6, ammonia is zero, nitrates 5-10ppm, and nitrites are high at at least 5ppm (the upper limit of the scale on my liquid test kit). I am anxious to add some new residents, but of course will not until the tank finishes cycling, but my question arose after a visit to my local fish store where I asked for some guidance with the nitrite spike. I have been treating all the water with Prime at weekly 10-15% water changes, as well as two extra 1 teaspoon treatments for the whole tank. Nitrites remained pegged at 5ppm throughout. This seemed to alarm the fish store associate, who strikes me as generally knowlegeable. He said that it was really unusual to have such a big, resistant nitrite spike even at startup, and urged me to hang a second 350 gph filter. My immediate thought was that, although you cannot really "overfilter" a tank, do I really need a second filter and its associated costs, or do I just need to be patient and continue waiting for the cycle to complete? He assured me that Prime would not interfere with the nitrogen cycle and to continue treating the whole body of water until the nitrites were under control. He would not tell me, when pressed, exactly what he meant by continuing to treat with Prime. How often can I safely dose the tank and how often? He didn't seem to want to be responsible for giving me specific instructions. So, is my tank adequately filtered, in your opinion? My priority is fish well-being, and I am nervous that the nitrites are stressing out the danios, but my inclination is to remain patient as the fish seem to be fine. Thanks for your consideration!