pretty much same stock list as my 100g (- rummy nose, cockatoo & hatchets) works well and as you believe if you get young Angels they are less likely to see cardinals etc as snacks - not a garuntee though! I wouldn't trust cardinals with the 6month ols in the 30g!
As for gravel make sure it's not to sharp and is nicely rounded for your cory's - they have delicate whiskers (can't think of proper term!) Can't comment on sand as I used a really fine grade gravel but i hear it can stagnate and cause anaerobic pockets which could result in some nasty toxins being released. A substrate heating cable would prevent this as makes the water flow around.
As for the Sump - PM AshDavid he has some good ideas he posted a pic in a thread but i can't find it.
As for gravel make sure it's not to sharp and is nicely rounded for your cory's - they have delicate whiskers (can't think of proper term!) Can't comment on sand as I used a really fine grade gravel but i hear it can stagnate and cause anaerobic pockets which could result in some nasty toxins being released. A substrate heating cable would prevent this as makes the water flow around.
As for the Sump - PM AshDavid he has some good ideas he posted a pic in a thread but i can't find it.
