I planted it three nights ago,
with what I would call a moderate plant load.

If you only planted it three nights ago, the plants may not be established and
growing well yet.

o ammonia/ammonium: 0.5ppm
o nitrite: 5.0ppm

Wow. I wouldn't expect four corys in a 55 gallon tank to produce that kind of
nitrite spike. That is a dangerously high level.

Is it normal for the plants to have to establish themselves
first?

Yes. Especially if they are rooted plants, like swords and crypts.

Also, just in the last couple days, ammonia/ammonium has gone
from 1.0 to 0.5 ppm and nitrite up from 0 to 5.0 ppm. This is good right?

Well, it sounds like your tank is cycling. However, it sounds awfully rough on
the fish. Especially corys and a tetra fry, which aren't known as the hardiest
of fish, at least when it comes to water quality.

Next time, I would consider either doing a "fishless cycle," or using Chuck's
method for planted tanks:

http://www.csd.net/~cgadd/aqua/art_plant_newtank.htm



Leigh

http://www.fortunecity.com/lavender/halloween/881/