Kelvin -
     the PMDD recipe is at 
     and is attached to a document on algae control as an appendix.
     I have been trying to get a hydroponics shop to mix me up a batch. I 
     have also been talking to Paul Sears and Pat Bowerman about the actual 
     chemistry mixture, and I have also been talking to James Wong. Thanks 
     to all three for their help and their patience. 
     Not being a chemist I have found the PMDD recipe to be fairly 
     confusing. It transpires from several exchanges that the percentages 
     of trace metals listed as part of the PMDD recipe do not refer to the 
     chelated metal complexes themselves; rather, I THINK they refer to the 
     amount of metal delivered by the chelated complex once the complex is 
     'active' in solution. 
     This is to say that if you get a TE mix recipe that calls for 7% Fe 
     (as the PMDD recipe does), and you make up a mix that contains 7% Fe 
     chelate, you don't actually end up with 7% Fe in the water and 
     available to the plants. You actually end up with a considerable 
     anmount less - as Pat explained it, you end up with about 1.5% Fe 
     available to the plants. 
     I find this very confusing, and I'm still not sure that I have this 
     right. I also suspect that I'm not the only one in this situation. 
     Perhaps someone could help us spuds out a bit with a detailed 
     explanation of how to explain this arrangement to a hydroponics shop.
     On a slightly different note I found at 
     a recipe provided by Shiao Y. Wang in 1995 for a trace element mix 
     which apparently is a plant tissue culture media. It's comprised of 
     EDTA sodium ferric salt    40g
     Na2MoO4.2H2O               250mg
     H3BO3                      3g
     MnCl2.4H2O                 10g
     ZnSO4.7H2O                 2g
     CoCl2.6H2O                 25mg
     CuSO4.5H2O                 25mg
     per litre (of distilled water?). The dosage rate is given as 30ml per 
     30 gallons of water in a 75 gallon tank but I would assume this would 
     need to be varied to suit individual tank conditions.
     Personally I find this recipe great deal easier to get my head around. 
     I also imagine that it will be easier to ask a hydroponics shop to mix 
     up (say) half a kilo of this stuff, keeping the proportions even. I 
     have been told that these things should be readily available at most 
     chemical supply shops and, by multiplying the amounts given above by 
     (say) 100, the average chemically-illiterate punter like myself should 
     be able to put the mix together. 
     Any comments would be extremely welcome.