I talked a little bit to Greg about something related to this a while ago. I mixed a 1.25% Fe mixture by using CSM+B. The next morning I had significant rocks form at the bottom that could not be dissolved. I know dilute the stuff much more. He said PMDD is hard to mix at the recommended dilution.
Try diluting the stuff the next time putting the ingredients in 900 ml of water, and use a 3x dosage.
What I do now is add 36.9 g of KNO3, 17.7 g of CSM+B, 11.4 g of a 10% Fe DPTA compound and 3.3 g of KH2PO4 to 3 quarts of water (a 3 liter soda bottle will hold it). About 1.7 ounces per 10 gallons will give me 10 ppm NO3, .75 ppm Fe, amd 1 ppm PO4.
With this dilution the solution never clumps up.
Steve Pituch