Thanks Wasserpest, I ordered a phosphate test kit from Bigalsonline.com. BTW, the reds I like, but its the browning at the top I don't like. Not to mention the stems starting to grow sideways kind of bug me, too.
Also, Gregg, you must be right about it being thread algae, because there are some pretty long strings in a few places. I added NO3 to bring it up to 10ppm and tested 4-5 hours later, and it tested again at 5ppm. Is it possible for plants to take in that much NO3 so quickly? I noticed the Cabomba, Myrio, and Mexican Oak have all grown about 7"-8" in height in the last 2 weeks (everything else is growing rapidly, too), which seems tremendous to me.