not too much more to say, Rex gave most info needed.
1. It's a DIY fert mix. One of it's components IS Iron (unless you've found an odd recipe). The initial trace minerals mix (Usually Plantex CSM or CSM+B) contains the Iron.
2. Use a good plant substrate, and if you need, add in fert-tabs.
The DIY pmdd setup is usually quite cheaper than anything commercial.