First... if you have raised a lot of angel fish, you will be used to the term '9th Day Syndrom'. For some still unknown reason (or more than likely a million small reasons) MANY batches of angelfish will sudenly have a huge die off on or right near the 9th day of free-swim. Very experienced breeders still sometimes see this. I personally think a lot of it has to do with the fact that some batches of eggs will be less developed in-fish before they are layed, leading to extra small fry that simply can't eat food even the size of fresh hatched brine shrimp... on or about the 9th day they run out of their fat stores from the egg sack and boom... 95% or more die at once.
With that in mind, I don't really think your corries ate the live ones, but maybe munched up all the ones as they died.
Second... I have vacumed many-many angel babies in lots of different stages and never had a problem with it damaging more than a couple.
Also, as long as you keep good water params, a ton of water changes really arn't nessesary as long as you have a good bit of plants and some snails. Snails eat up leftovers... make poo... infusoria thrives on snail poo... baby fish (especially ones as small as angels) need to eat infusoria for the first few days of eating... plants clean the water and give infusoria and bacteria a place to grow.
I also move my babies from small tanks (2.5g) up gradually in tank size when they start to need a bigger tank. It is especially usefull to have a small tank for the babies to start with, since the food is concentraited all around the babies while they are too young to hunt all over a bigger tank for it.
I have about 200 babies in one 2.5 going on 3 weeks now, and they will be moving up to a bigger tank this week.... lots of plants.... about 10 snails... sponge filter powered with bubbles.
Of course, I am a stay at home fish-parent, so I feed them micro worms many times a day and have only lost a few babies from this batch (took maybe 225 or so from the parents just before free-swim).
For a good regulating heater for a tiny tank, I get the ones sold at Wal-Mart. They are (Tetra) Whisper Heater, submirsible (great since you don't have to mess with them during a water change) for 2-15 gallons, Pre-set (to 78). They are really small and have done a great job keeping a tiny tank spot on temp even though our house fluctuates from 73 during the day to 63 at night.
Well, I have blabed on long enough... LOL I get so long winded when it comes to fish. :icon_lol: