If by clean it you mean you remove everything from the tank and rinse/wash it off, by doing that you are starting the cycle all over again. The cycle happens in every new tank, and as Marie said, once it's cycled, you won't need to add any more bacteria.
It looks to me like maybe you have a couple of things happening here.
1. When you do water changes, you need to treat your water with a product like Amquel (removes chlorine and chloramines). It only takes a teaspoon to treat 10 gallons of water, and you only have to treat what you change. Meaning, if you change a third of the water in a 30-gallon tank, you only need to use one teaspoon, not three.
2. The cycle takes about six weeks, sometimes longer, to complete in most tanks. Here's how it happens: your fish produce waste, which is in the form of ammonia (food rotting also does this). Ammonia is very hazardous to fish, which is why you want to be extra careful with water changes and monitoring the tank during this time. Soon, though, nitrifying bacteria grow in the tank, and those bacteria turn the ammonia into nitrites, which are harmful to fish, but not nearly as harmful as ammonia. Then the tank will grow other bacteria that turn the nitrites into nitrates. Nitrates are harmless at low levels, but the only way to get rid of them is water changes (or live plants, but that's a whole 'nother topic).
So, in short, ammonia (provided by fish) becomes nitrites, which becomes nitrates. If you clean everything in the tank, you kill the bacteria that do this, and it all has to start over again. Unless you have a diseased tank (and most of the time not even then), it's not a good idea to break down your tank and start over.
If you get some Amquel, make sure you have appropriate filtration, and continue with your water changes (maybe smaller ones every week would be better, especially while the tank is not yet cycled), you should be fine. I would stay away from getting any delicate fish before the tank is cycled. Neons, for instance, are not really the beginner fish they are touted to be; the little buggers are actually quite difficult to keep alive.