I agree with most of what has been posted, but there are some major issues too.
First, the rams. These fish need warmth, no less than 82F. This is fine for the cardinals, but not the corys.
Corydoras panda is a cooler water fish [click the shaded name for the profile]. The
Guppy would be at the high end of its preferred range, which is not usually the best, as this means the fish is working harder all the time [higher temp = more effort to "live"].
Water parameters are key here, as the cardinals will not last in harder water. The ram needs whatever they were raised in, check that profile [click
Blue Ram].
On the substrate issue, I would agree that corys often have trouble with Eco-complete and the very similar Flourite.
Byron.