Re:Nutrients & Hydroponics vs Aquaculture

     >After talking to various plant people, it was interesting to note 
     >that the levels of trace element in the PMDD mix vs. most hydroponic 
     >trace mixes are 20 to 1,000 times as much.  Does anyone know why we 
     >would need (for example) 1,000 times more of an element in a fishtank 
     >vs. hydroponics (which seems to me to be the same minus the fish)?
     Yes, the product concentration is lower, but the amount (volume) you 
     actually USE is more.  I do not know why the stock solution of some 
     hydroponic fertilizers is so low (maybe so they can sell more units?). 
     The actual concentration of N-P-K and trace elements in the hydroponic 
     growth medium is higher than we would dare have in our tanks.
     I inquired about a 7% chelated iron-trace element mix at a hydroponics 
     store once, and the clerk was astounded--"500 grams of 7% Fe?!?!?!?  
     Why, that would last you for YEARS!!!!"  Another clerk tried to 
     persuade me that 7% Fe would be toxic.  
     It's also worth noting that the American hydroponics shops sell mostly 
     dilute, liquid fertilizers, very little powder.  If you work out the 
     costs, you are paying a pretty penny to have (mostly) water shipped to