Here we go folks,
Taken from Jon's first post on his tilapia arrive thread.
This may help.
I'm also curious as to why your nitrates are up so high, I suspect your system has not cycled yet, and would expect your system to have high nitrites at this stage but I don't know why such a high nitrate reading.
Maybe others can answer that for us.
What's your ammonia reading and tank temps? It just helps form a bit more of a picture for us as pH, ammonia, and fish tank temps have an effect on each other in regards to toxity to your fish.
The other thing I would suggest is to take a set of readings of your pH,nitrites ammonia,nitrates and fish tank temp today and post and see if there is any difference.
You could also look at my water testing thread in the general aquaponics discussion section, for when I cycled my trout system, I had high nitrites for quite a while and was concerned. It was a little different to your situation, I had no nitrates though, but a read of that may help.
Regardless I'd do what the otheres are suggesting They helped me when I first cycled.