Ammonia testing and cory questions?

Okay, a few questions:

1.) My 10 gallon tank is very tannin stained from the driftwood I have in there. Unlike most people, I really like this effect. However, it does present a problem--how do I test for ammonia/nitrite/nitrate? The brown water distorts the test colors, and I'd rather not use strips since they're not as accurate.

2.) This is going to sound like kind of a strange question, but...I've got 3 bronze and 5 panda corys in my 20 gallon, and they both spawn almost EVERY night, especially the pandas. They can't wear themselves out doing this, can they? Will this overly stress the females? They all look fine, are very active and eat like pigs, and I certainly don't know how I could STOP them from spawning. I know it's normal for corys to spawn all the time in fish tanks, and it's cool to watch, I just want to make sure it's not causing any stress, primarily for the females. Again, I know, weird question--I'm just paranoid about my fish, heh.