Trying To Go Tropical

[tricky8]

hi all i had a 25l golfish tank that i am trying to turn tropical
i have mature gravel ,a heater a filter that only has a white sponge in so no biomax nodes or black filter just as i say a white sponge
its been fishleess for 7 weeks now and i have been diong water tests and nitrate 40 nitrite 0 ph 7.5 and ammonia was 0.25 now after water changes got it to 0
i been conditioning the water on every water change and by the way it has nothing in it except ornaments ie no plants or wood
i put 1 platy in there out of my own big 90l tank and its died
i installed a timered light as well so
just dont understand where am i going wrong
i feel like my filter isnt ok for tropical?
any furhter suggestions

 

[tricky8]

nothing?

 

[Essjay]

You say the tank has been fishless for 7 weeks. Do you mean that it just ran with no fish in or that you have been adding ammonia for the 7 weeks?
Mature gravel will have done nothing for the tank unless it came from a tank with an undergravel filter. Though without food in the form of fish waste or ammonia, even if the gravel did come from a tank with a UG filter, the bacteria would have died.

Could you let us know what you added to the tank during the 7 fishless weeks? When the platy died, what were the ammonia and nitrite levels?