What sort of filter do you have? All you need do is hang the filter in the main tank. When you are ready to put the female in the little tank, use water from the main one (or 2/3 - 1/3 as you did before) and add the filter, which will have cycled.
If you set up a tank with water and no fish it will not cycle if an ammonia food source is not being added.
I suspect not enough water changes compared to the amount of food being fed. Daily water changes would be better. Food is a little, often. Remember how small fry are - their stomachs are even smaller!