toxic fish

Nh3 Nh4 always at 1.5 ppm

Hi guys, seeking some advise pls。Using the JBL Nh3/Nh4 tester, my reading is always at range of +/- 1。5ppm This is very consistent on all 3 4x2x2 aquariums。 Each houses an 1 aro, 1 tankmate, 1 sucker...