First off sorry this is going to waffle just over 3 weeks ago I tried to be a minnow savior, we went to the local garden centre where minnows were being kept with goldfish and being eaten alive!!! As I had a spare 60 litre tank at home I purchased 6 and set it up when we got home with everything from our established 10 month old 210 litre goldfish tank (before this experience I knew nothing on cycling a tank or tank sizing ) Unfortunatly 2 died and stupidly other half bought 3 guppies. I have been testing daily ammonia, nitrites, nitrates and PH. First 2 weeks there were levels of ammonia between .5-.10 and have done daily 15-20% water changes with gravel hoover. On Saturday and Sunday there were levels of .25-.50 nitrite. Now for past 3 days ammonia and nitrite at 0 and nitrate at between 5-10ppm. Has this tank cycled so quick because of the use of media and substrate of establised tank or am I being delusional?