I have a 40g tank stocked with 1 rummy nose tetra (2 have died), 1 pleco, 3 platys, 1 molly, 5 rasboras, 1 rainbow shark (not full grown). My last readings were Ammo 0, NitrIte 0, pH 7.6, nitrAte 40. I have done 2 water changes with gravel vac since the last reading. That was 4 days ago...