Don't add anything to the tank without some objective evidence telling you that you need it. If you don't have nitrite, and you have nothing to measure ammonia, then you have no evidence to say that your beneficial/nitrifying bacteria need "Quick Start".
You have 5 large Sev's, and then 10 other medium fish. You have what sounds to me like a pretty heavily stocked tank. You should get a liquid ammonia test. Also, SeaChem makes a strip that goes inside the tank. If it measures ammonia it changes color--tells you if an ammonia spike has occurred. Get that, too--they're cheap. With lots of fish, you may not realize you're having ammonia spikes after feeding.
In the meantime...do nothing. Don't change anything, don't clean things, nothing. Start figuring out if you're gonna get a new tank, or re-home some fish. Measure ammonia/nitrite/nitrate/pH and post it here. That's it.
You have 5 large Sev's, and then 10 other medium fish. You have what sounds to me like a pretty heavily stocked tank. You should get a liquid ammonia test. Also, SeaChem makes a strip that goes inside the tank. If it measures ammonia it changes color--tells you if an ammonia spike has occurred. Get that, too--they're cheap. With lots of fish, you may not realize you're having ammonia spikes after feeding.
In the meantime...do nothing. Don't change anything, don't clean things, nothing. Start figuring out if you're gonna get a new tank, or re-home some fish. Measure ammonia/nitrite/nitrate/pH and post it here. That's it.