It sounds as if you need to stop the water changes as long as the fish don't appear to be struggling. This is where learning the nitrogen cycle comes into play. The bacteria need some ammonia to feed on in order to produce nitrite. Nitrite is the waste product of the bacteria that feed on the ammonia. Then more bacteria feed on the nitrite, their waste is nitrate. If there is not ammonia in the tank long enough to feed the bacteria, the colony will die out... so when you eventually back off of the water changes, you will be starting from the beginning all over again and the culture you got from your lfs will have been pointless.
When a tank is fully cycled it will have produced first ammonia, then ammonia and nitrite at the same time, then no ammonia and some nitrite, then nitrite and nitrate at the same time, until eventually everything is fully broken down and there are enough bacteria to keep up with what waste is in the tank, leaving you with only nitrate showing up in the tests. So a healthy, cycled tank, should read 0 ammonia, 0 nitrite, and nitrate of 20 or less. It is possible to prolong the cycle by removing all ammonia as soon as its in the tank, which is what it sounds like you're doing. The longer you prolong the cycle the longer it will take before you can safely add more fish.
At this stage, cycling with fish... the only time you will want to do water changes is if the ammonia spikes very high and it appears to be affecting the fish. If the fish seem to be doing fine, then best to leave it alone and let nature take its course. Keep feedings light, only as much as the fish can completely finish within 1 minute, and only once/day. Anything beyond that will add extra waste to the tank because it begins to break down so quickly... and that can lead to danger levels for the fish. During cycling your tank should be adjusting to accommodate the amount of waste that the fish and food are putting into the tank.
The cycling period, even with fish, averages about 6 wks. If you have not starved the bacteria culture you got from your lfs, then I would expect that same time frame. If you have starved the beginning culture, the tank may take longer to cycle, and the ammonia levels may go higher than they would otherwise (while waiting for new bacteria to get started). If you write down the test results and continue to test every day or 2, you should be able to see the changes taking place.
If your fish begin acting "different" such as sitting on the bottom of the tank, or hang out at the surface gasping, get lethargic and inactive, stop eating, or have any dramatic change in color, then its time to check your water with the tests and post here so we can help determine if water changes are indeed needed, and how much and how often. Thats what we're here for... we will coach you through this 1 step at a time. If the fish continue to act fine, then don't worry. Tiger barbs are pretty sturdy fish and are often used for cycling. If you keep the amount of food to a minimum, there should be no reason for the waste levels to cause them an issue.
Hope this helps.