Hey man the best thing to do is wait one week and ad 3 or 4 neon tetra's by my standards the cheapest, hardiest fish. I even added six neons in to my 90 litre tank a day after adding water and mate they are still living to this day 6 months later. So my advice is wait one week and a fish. From then the ammonia , nitrate and the nitrite should all balance themselves out and also for the first few weeks add a solution which will add bacteria into the tank (I cant think of the one I have but when you see it you should know what it is). Then just a last tip dont get flake food it is very low in protein and is processed to with an inch of its life so always go for pellets or what your local fish store recommends.