You need to be doing a 50% WC
weekly to add fresh buffers back into your tank and to keep nitrates down to at least 20ppm or less. Also do you gravel vac when you do WC
Have you Ph tested your tap water? In order to do that you need to put tap water in a cup and either aerate it or stir it off and on for 24 hours to gass it off. After 24 hours you can take your Ph on it and this will be your taps true Ph reading.