How did you cycle your tank? Do you understand the basics of the nitrogen cycle ?
Aiken drum should be chiming in here soon. There’s a whole phone book that’s put together about the nitrogen cycle that is a great read for beginners
Basically unless you used cycled filter media from an established tank, you didn’t cycle your tank in 2 weeks.
What were the ammonia levels in your tap water? How many fish in the tank?
Unfortunately if you’ve got more than a few fish in there you’re going to need to do quite a few water changes before the tank cycles which is going to be 4-8weeks from the time the ammonia source (fish food and waste) is added to the tank. Large regular water changes aren’t very practical if they can’t be done with tap water. But if you’re tap water only tests minimal positive for ammonia (under .25ppm) I would just go with that and do more frequent water changes.
There’s a few factors at play here. The higher the water ph and the higher the water temperature, the more toxic ammonia is to the fish. Generally your safe up to the 1ppm range and if you can keep it under that you should be able to get through till the tank cycles. If you were at 4ppm and only changed 25% water you’re still way above an acceptable level for any condition, at 4ppm you’d want to do at least 75% water change to get it down to 1ppm then another 50% water change shortly after to get it down to a more acceptable level.
As you can see, it’s going to take quite a bit of water to maintain water quality in the tank until it’s actually cycled. So, say you’ve got .25ppm ammonia in your tap water, it’s not ideal, but in this case with enough water changes you’ll be able to maintain ammonia under 1ppm without having to lug 5000gallons of water through the house in the next few weeks!
I don’t want to scare you, but you’re probably in for a bit of work till the tank is cycled. This is honestly a daily scenario we see here, fish shops either don’t know or don’t care about educating the customer. They just want to sell the tank and fish and send you on your way. If you’ve got a bit of time to devote to the tank for a few weeks it’s really no big deal, I fish-in cycle my tanks and even going full dummy mode and throwing almost 40 comets into a 36gal to cycle was still manageable with daily water changes