Nitrate and nitrite problems

Question
Hi Alex,
I have recently set up a 4ft freshwater fish tank. I am using an eheim 2213 filter. After letting it cycle for 9 days I got 8 fish - 2 small catfish, 6 full grown guppies and 2 baby guppies. Within a week I had extremely high levels of ammonia nitrate nitrite. I was putting in cycle each day. 4 fish died in two days and I now have the 2 babies, 1 guppy and 1 catfish left.
I then placed a nitra-zorb pad into my filter which lowered my ammonia levels down to zero but my nitrate and nitrite levels are still off the scale. The aquarium shop has suggested that it must be the gravel (which is black and purple) because everything in my tank has turned purple and when the same gravel was put in established water within the week the nitrate ad nitrite levels were high.
The shop i got the gravel from is telling me its impossible. Can you give me any other reason for these levels?
Today i have removed the gravel in the hope that things settle down!
Thanks for any advice you can give me!

Answer
Gravel should do nothing to the nitrate and nitrite so those knuckleheads saying that are out of their minds. You should always though rinse your gravel in order to avoid coloring on other things. Do water changes and get a bio wheel and continue the use of cycle.