Excellent advice from rebrn and the others above! Well done!
It seems to me you are in a fish-in cycle/ammonia spike. The reason why I said ammonia spike is because your nitrite level is still at zero, as for now that is. Also, the Filter Start is no good. You can continue to use it until it is all gone, or just stop using it all together.
Also, I see you have not been doing gravel cleaning with a gravel vac, this could possibly be the main reason as to why your ammonia is so high right now. When you do not clean the gravel, which should be done weekly during you weekly water change of 10-20%, fish waste, dead and decaying plant matter and other debris settle on the bottom of the tank. When this happens, the fish poo and other what stuff began to produce ammonia. Over time, 6 weeks in your case, there is going to be an exponential increase in the ammonia produced from this rotting matter at the bottom of your tank, which could be where you ammonia spike is coming from. So, you need to get a gravel vac at your fish store, any will do! Just as long you swift through your substrate and get all the poo and debris out.
"What is cycling?"
Like stated above, cycling is colonizing enough bacteria in your filter, these bacteria process ammonia and nitrite, to safely handle the ammonia that is given off by your fish. In the beginning, there is not even close to the amount of bacteria you need, so it takes time to colonize these bacteria. First, when ammonia is produced, the first type of bacteria process the ammonia. When ammonia is processed, it turns into nitrite. Now, a second bacteria begins to colonize. This bacteria processing nitrite into nitrAte.
Ammonia and nitrite are toxic to fish if one, or the other, exceeds .25 ppm! Ammonia at or above .25 ppm will cause permanent gill damage, while nitrite at or above .25 ppm will cause permanent nerve damage.
In a fully cycled tank the ammonia and nitrite will remain at 0 ppm, because of the bacteria. At this time, a fully cycled tank, there is enough bacteria to process the ammonia and nitrite, and keep them at a constant 0 ppm.
Nitrate, the final product in the cycle should not exceed 20 ppm above your tap water. If you have 10 ppm of nitrate in your tap water, then you do not want more than 30 ppm of nitrate in your tank.
"Where am I at then? What do I need to do?"
First of all, do not buy any kind of product that claims it removes/neutralizes ammonia! Removing the ammonia source in your tank will cause your beneficial bacteria to die off! Bad bad!
Right now, there is not enough of these beneficial bacteria in your filter, (Yes, these bacteria colonize in your filter, not in your water column.) to keep the ammoina at zero. So, since you have fish, which means you have a constant source of ammonia, you need to take action by doing large water changes! You need to do enough water changes to keep your ammonia and nitrite levels as close to 0 ppm as possible! Do not let them exceed .25 ppm!
Over time, more and more beneficial bacteria will colonize in your filter to process the ammonia and nitrite for you! Once your ammonia and nitrite remain at a constant 0 ppm for a week, without a water change, you can consider yourself cycled! Be ready for a couple weeks of solid daily water changes, as it takes time for these friendly bacteria to colonize in your filter!
I hope this clears things up a bit for you!
-FHM