I would say you are over stocked and this could he causing the fish to be stressed and nippy.
Danios, neons, penguin tetras, runnynose tetras and the clown loaches all need to be in groups of 6 or more, this could also be causing the problem...
Also, the clown loach will get far too big for a 96 litre...
This is why your nitrates are quite high also...
Sorry to be a downer but i would say that re-homing or selling some of these fishies would make the ones you keep a lot happier
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