I've had my tank for 13 weeks. At first I had 6 zebra danios after a day and adding tetra safe start from advice from my LFS. Long story short, they're dead and I'm not cycled after 13 weeks. I've tried everything. I have: 20 gallon tank, the top fin complete kit so I'm not sure what filter it came with. Temp 79 Amm 2-4ppm Ph 7.8 Nitrite 0 Nitrate 0 All other factors are good according to the test strip. I test the water with API test kit and tetra easy strips. Two weeks ago I tried adding seachems stability. Nothing has changed. I'm about to quit. Any advice? I did water changes when I had fish, but they died anyway.