Nitrates are the final product of the cycle and are toxic to fish at high levels. They are removed and kept under control by regular partial water changes.
For most typical community fish maintaining nitrates below about 40ppm is fine; less than 20ppm is ideal. In some cases though, the water supply has up to 50ppm already in it at the tap so for those in that position, maintenance at no more than 20ppm above tap level is OK as long as particularly nitrate sensitive fish are avoided.
My tap water has 40ppm of nitrate and that is one of the reasons I use RO water instead of water straight from the tap.
Thanks, I'm presuming my tap water will be naturally low in nitrates due to the low level or could that be the good bacteria keeping that low?
I'll test some tap water tonight to confirm.
Also this will be a silly question however as a beginner I can be forgiven haha
My tap water is really cold and obviously doing a 50% water change tonight will drastically change my temperature in the tank. I am thinking of adding a boiled kettle to every second bucket of water to combat this unless there are any other suggestions?
Ammonia and nitrite should be 0, nitrate up to 40ppm. You won't see nitrate at 0 in a cycled tank as the continuous conversion of ammonia to nitrite and nitrite to nitrate means it is ever present. Even partial water changes can't reduce nitrate to 0 as you'd have to change 100% of the water for fresh water with a 0 nitrate reading to get there. A small amount of nitrate is no problem and is even helpful for your plants.