Er, do you know what the natural diet of angelfish is? It's neons. Might want to re-think your stocking options.
The "little red fish with black triangles" aren't platies, by any chance are they? Or maybe some kind of rasbora? Either way, they are shoaling fish so should be kept in groups of at least 6-8. I suggest you buy a few more of them (having identified what they are first, of course!).
I'm not familiar with anything called a "tiger loach", but the behaviour you've described worries me. Would you happen to know its Latin name? I'm thinking maybe you need more angelfish, but I'm also worried that think ain't no loach.
If the "big catfish" are Common Suckermouth Plecs then 6-7 inches isn't even a teenager yet - wait until they get to full size. I hope you've got a really big tank.
I suggest you try to identify exactly what you've got and let the members of this forum have a look at it, before buying something else. We could probably save you some grief ;o)
As for test kits, personally I'd get something to test for ammonia, nitrite, nitrate and a general box of eSHa multisticks. You definitely need to test your water before you buy anything more - you tank may not be cycled yet or it may have a nitrite spike when you add new stock.
to the forum!
What fish are you keeping?
