I'm assuming you meant nitrite, not nitrate? If you did mean nitrate, then that means your tank isn't cycled.
If it is cycled, then I would next wonder if you have a substrate? I found that when I tried no substrate, my water was constantly super cloudy. That's because even though most of the bb is in the filter, there is still a layer that grows on everything. If there's no sand on the bottom, then it gets stirred up every time your axolotl moves. Adding sand helped for me, I specifically really like the super naturals Caribbean Tahitian moon sand something or other. It's the one that is the colour of actual golden brownish beach sand, it's inert, and it's a very fine grain. It's good for keeping the waste on top at first, but absorbing it in a healthy way if you miss it.
Something else that helped me, which is controversial probably, is adding a filter feeder. I have a fresh water mussel I plucked out of a local river a year or so ago, and had it in a crayfish tank up until a month ago. My cray died, so I put it in my axolotl tank and the water is crystal clear now. Since it's unlikely you have access to these, I recommend bamboo shrimp. They are filter feeders in much the same way, but I wouldn't get them unless you have a big tank with a lot of plants (and can afford to lose a couple potentially)
