For heavens sake, don't waste the start you've made on the bacteria you need - refill the tank and start feeding it with ammonia or fish food, assuming your filter's still OK and hasn't been dried out or off too long.
You do (or did, depending) also have beneficial bacteria in your gravel; studies conducted by biologists show that such bacteria tends to be drawn toward, and adhere to, nearby surfaces and as long as sufficient oxygen, food and, of course water, is available, these will propagate and adhere to all suitable surfaces (even smooth surfaces such as plastic, once a biofilm has formed over it) in your tank.
If your filter's been off too long or the media's dried out, you may have lost the bacteria there, but some may have survived in your gravel, if enough water remains on top, and any start made hastens the cycling process.
http
/www.aquariumfish.com/aquariumfish/d...788&search=
... Probably the biggest repository of helpful bacteria in your aquarium occurs on the surface of each piece of gravel. Each grain, though appearing smooth to the eye, is rough at a microscopic level, and thus provides a huge surface area for the growth of helpful bacteria. So, it follows that if you sterilize your gravel, you will destroy most of the biofiltration in your tank. Not knowing this, hobbyists sometimes remove the gravel for cleaning and have been known to boil it, scald it or (worst of all) use bleach or soap to sterilize the gravel. This is a huge mistake! It kills off the nitrifying bacteria and will allow ammonia levels to increase rapidly in the water. Gravel should never be cleaned with anything but plain, aquarium-temperature water. ...
... Safely Maintaining Filters
The most significant part of your aquarium maintenance is likely to involve the cleaning of one or more filters. Filters don’t remove waste — they just collect it. Nitrifying bacteria grow on every solid surface in the tank, including gravel, glass, plants, decorations and filter media. Indeed, most filters contain some type of biomedia designed to provide plenty of surface area for the growth of helpful bacteria. So, it’s best to take steps to preserve the bacteria on this media when possible. ...
Populations of organisms typically increase in relation to food supplies, or any other essential the lack of which forms a limiting factor.
Fish having been in that tank, it would have been seeded with bacteria merely needing time and essential supplies to achieve population levels sufficient to process the desired/supplied amount of 'nutrients, i.e., variously ammonia and nitrites converted by different bacterial types.
