Cardinals are a really bad fish to try and cycle a tank with. They are super sensitive to water changes / ammonia / nitrites. Definitely 1 of the more difficult tetras to keep.
I agree with most of what has been posted - you want to keep up on partial water changes while the fish are in until the tank is cycled. Change enough each day to keep ammonia and nitrites below .25.
I have had good luck recently with a product called seachem stability. It has done a great job in speeding up my cycle. After just about 1 week, my tank is just about through the cycle, with no fish loss, and only 1 partial water change.
What is the pH of your tap water? If your tank pH is below 6.0 I am guessing you have injected way too much CO2. If you post your pH and KH readings, we can tell you what CO2 concentration you are at. I don't think there is anything wrong with running the CO2 while you are cycling, but you want to aim for 25-50 or so PPM of CO2.
Your lighting ought to be adequate, maybe even too much. I would reduce your photo period to around 8-10 hrs a day to start or you may end up with a bad algae problem. You can always dial it up from there.
Also, your bulbs are not optimum for plant growth, though they will probably work. Research shows the best color temp to be between 6500K and 10000K for plant growth.
Plants need light that peaks in the red spectrum. As you go up temp scale, you tend to get more peaks in the blue spectrum. The optimum temp for aquatic plants is generally considered to be around 6700K. This is a close analogue to light on a sunny day. It is a good compromise of good red spectrum peaks, and still looks natural so your aquarium looks great. As you move up towards 10000K you are getting into light range analogous to an overcast day. Not optimum but still beneficial to plants. As you go above that you move more into the blue peaks of light... good for coral, not so much for FW plants.
I agree with most of what has been posted - you want to keep up on partial water changes while the fish are in until the tank is cycled. Change enough each day to keep ammonia and nitrites below .25.
I have had good luck recently with a product called seachem stability. It has done a great job in speeding up my cycle. After just about 1 week, my tank is just about through the cycle, with no fish loss, and only 1 partial water change.
What is the pH of your tap water? If your tank pH is below 6.0 I am guessing you have injected way too much CO2. If you post your pH and KH readings, we can tell you what CO2 concentration you are at. I don't think there is anything wrong with running the CO2 while you are cycling, but you want to aim for 25-50 or so PPM of CO2.
Your lighting ought to be adequate, maybe even too much. I would reduce your photo period to around 8-10 hrs a day to start or you may end up with a bad algae problem. You can always dial it up from there.
Also, your bulbs are not optimum for plant growth, though they will probably work. Research shows the best color temp to be between 6500K and 10000K for plant growth.
Plants need light that peaks in the red spectrum. As you go up temp scale, you tend to get more peaks in the blue spectrum. The optimum temp for aquatic plants is generally considered to be around 6700K. This is a close analogue to light on a sunny day. It is a good compromise of good red spectrum peaks, and still looks natural so your aquarium looks great. As you move up towards 10000K you are getting into light range analogous to an overcast day. Not optimum but still beneficial to plants. As you go above that you move more into the blue peaks of light... good for coral, not so much for FW plants.
