Why wont the bio-cycle start?

[Mike62]

I am having a problem getting my biological cycle to start in my tank.
First of all, the tank was converted from salt water to fresh water, about 2 months ago. At that time, all the filter media was thrown out as it was salt water media. The tank sat empty of fish (there was water and circulation through the filter), once in a while, I tossed in some food, hoping it would rot and create the ammonia needed to start. Ammonia, nitrate and nitrite levels remained at zero. After a month of nothing, I started by adding a product called "Cycle" and added a few cichlids. There are now 7 cichlids in the tank. The ammonia level has risen to .5PPM, however the nitrate and nitrite levels remain at zero. They have never moved up, and thats testing at least twice a week.
There are bio balls in the filter, as well as a carbon and a sponge insert. The carbon was changed about a month into the operation, the sponge about 2 weeks ago.
Why am I not seeing the ammonia being converted to nitrate and nitrite. And is .5PPM ammonia low or high? The cichlids seem fine, swimming all over the place, probably harassing each other, and gathering like a pack of wolves when they see me coming with the food.

[Toss]

You are doing fine for now. Not to worry about the cycle. It will happen by itself. As long as you don't drop tons of fish in it at the same time, you should probably just sit back, relax and enjoy your fish you have in there

[Fishnut]

Keep testing, just in case.  Make sure you don't over-feed

[sas]

There are bio balls in the filter, as well as a carbon and a sponge insert. The carbon was changed about a month into the operation, the sponge about 2 weeks ago.

Just to add to what has been mentioned, don't change out your sponge,
just rinse it in tank water.
I use sponges and don't change them until they start to fall apart, a good rinse
in tank water is all they need.