The definition of a cycled tank used in fishless cycling is one which can process a 3 ppm dose of ammonia to zero ammonia and zero nitrite within 24 hours. The fact that you have a reading above zero for nitrite suggests the tank is not fully cycled.
It sounds as though running the filter in a mature tank did not grow enough bacteria for the livestock currently in your tank. If the other tank had a lot of plants, there would be less bacteria growing in there than in a tank with no live plants, so less to grow in your sponge filter.
Many bacterial starters contain the wrong species of nitrite eaters, so unless you used one of those which contain the right species that could explain why you have nitrite but not ammonia.
Any reading above zero for nitrite is not good for fish. It blocks the blood cells from taking up oxygen - it does to fish what carbon monoxide does to us. Until nitrite drops to zero, you need to do water changes to lower the level, or use salt, which mitigates the effect of nitrite. The second part of this link deals with using salt for nitrite.
Part II SO YOU STILL WANT TO KEEP CYCLING WITH FISH? If you are determined to ignore the above advice in Part I and still think you want to proceed with a fish in cycle, then you need to be aware of the information presented below. SOME IMPORTANT FACTS ABOUT AMMONIA Ammonia in water exists...
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