Been doing regular 30% changes, it's not ammonia, i've got 2 different kits & test every 3 days. Always 0ppm. 10 Danio, 8 Kuhli, 4 Tiny Otto & a baby Pleco couldn't produce an ammonia spike in a 250L tank if they tried, the filter is rated for 500L tanks too.
The tap water contains 55ppm...