Gold Smelly Urine Smelly Fish Tank Help ....please?

Smelly fish tank help ....please? - gold smelly urine

has placed in recent weeks in February and the container into the new house. We have a 20 gallon tank with 1> 4-5in gold fish in it. We help small 2 new plants in the air. We have a bio-filter wheel. I hadnt the chance to my normal 15-25% of water every 10-12 days, which I usually do not, and 15 days when it was found that the tank has lifted the lid when it was really bad. so I really put the water 70%, all figures in the tank, plants and cleaning of filters and all that ... I empty the rocks and cleaned the walls. then put everything back together. It was 2 days ago and went back to his food and is always a bad smell, not bad, but I can say. How to feed the fish 2 times a day, and there are usually no leftovers quickly, the fish that swallows! My water is crystal clear!
THAT is my problem!
HELP PLEASE!