Ammonia levels are high?

My tank is 3 months old, 29g freshwater community with 12 very small fish. I have an undergravel filter and a whisperflow power filter. My ammonia levels read 8 with an API reagent tester. I've used to try and control this with lots of ammonia remover and weekly water changes. I added ammo chips to my filter. I only feed them once a day and the food is gone in 90 sec. I use a gravel siphon the clean the gravel and change about 20% of my water every week. I asked for help a week ago and was advised to stop using chemicals, stay with ammo chips and do lots of water changes to get rid of the chemicals. So, I did, new tests reveal a pH of 6.8, nitrates read 20, nitrites 0 and ammonia 8. Help!!! I'm getting really frustrated. My fish seem unaware of any problem. Swimming around normally and eating as much as possible. What next? Ahhhhhhhhh!