Hi Adam,

I'm glad you like the towers.  They're my own design.  I'll post more photos for you soon.  It looks like you're on your way!

I raised tilipia in a 55 gallon barrelponics system for almost 2 years with no tests. I had 15 or so tilipia, and was able to harvest numerous crops including green beans, basil, lettuce, and tomatoes.  I don't know how long you "primed the system", but if you don't push it hard there is no need for test if you just want a little fish and some produce.  My system was taken off the web (search barrelponics).  There is no reason you should not have success using your tank instead of a barrel.  In fact I never did a water change on purpose (since most of the time I left the water hose on to long since I have no attention span).  I used city water with no treatments on tilipia.  The best thing to do is build your fish population slowly at first, and then go all out.  Once the bacteria is there it takes little to no time to adjust to the new inputs.  Your grow bed might be just to small if it was a water quality issue, or it might be something totally unrelated.  I was using 55 gallons of grow bed to 55 gallons of fish, but I was using pea gravel as the bed.  The only difference between our systems besides the tank is the media. The only difference between the different media is that hydroton and pea gravel take up different amounts of space and the surface area for bacterial growth.  You might have run into problems(most likely not) from the plants not being able to uptake nitrates fast enough since the plants in your pictures seem small(if not seedlings). 

If your system is really new:

The most likely cause of the death is not cycling properly. 

Solution:

Keep running the thing.  In a few days add 5 fish.  Wait a 5-10 days and add some more.  Make sure you buffer to 80-120ppm alkalinity and hardness (baking soda) so that carbonic acid does not become an issue when you get closer to full capacity.  And for a cheaper way to kill fish, use feeder goldfish.  They are only 10-20 cents each.