The fertilizer is not the way to go. Lowes has fine Vermiculite without miracle grow as POP pointed out. I found coarse Vermiculite and Perlite at a local garden center. One part each with equal water volume added was nearly perfect. 2 cups of each and 6 cups of water was a good level for my bins with light diffusers sitting on top of 1/2" pvc for support.

I used a wine cooler as well. It had a light installed which I kept wired in. I used a Herpstsat for $129 shipped. I also put a nice 12vDC fan in mine at the top wired to a rheostat and ac/dc converter for $15. Two feet of 11" Flexwatt fit perfect. I put a simple 6 outlet cord where the compressor was. That goes to a surge protector and a battery back-up that will run it for a few hours in the event of a power interruption.

I put a simple little remore temp/humidity sensor in there as well. It reads within 1F of the Herpstat placed one shelf lower and gives me the internal cooler humidity. Tubs will obviously be different as you can see from the condensation. This little rig has been running 24/7 since I built it about 2 months ago..... she is ready!!

It's a nice little set-up if I don't say myself

Herpstat 1 with remote sensor. Herpstat sensor under top shelf, remote sensor under second shelf:


Inside with fan/light on. I could fit one more tub under fan if I had to:

Back with power strip, AC/DC convertor and rheostat (on left). Fan is set to about 50% and moves a lot of air even at half speed. The chiller actually already had the rheostat box- I just replaced the rheosat for the proper rated rheostat for my fan.