All first class advise here!
You need to up those water changes regardless of what the test kit is showing. I could probably leave my tank for well over a week and they would remain the same and stable but that isn't the point. When you change the water it not only helps reduce the waste and toxic build up but also replenishes minerals and oxygen. I do 30 - 50 % per week. I usually aim to change 100% of the water over a week period. Those nitrates are too high in my eyes and need to be addressed and you should getting zero ammonia at all times. Good luck with it and keep us in the loop on how things are going. Once you have this sorted then Id try the live food option, if that's refused then as I've said previously you'll need to start digging deeper with regards to the cause.