How many fish would it take?

I have a 37 gallon tank and i want real plants in it, and ive heard if you have enough fish theyll produce enough carbon dioxide for the plants. i have 2 in a 5 gallon and my plants are doing great, and i have 5 in a 10 gallon and the plants are doing fine, but i have 16-17 in my 37 and my plants are dying.. how many more should i add?? and what kinds