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PMDD Not Dissolving

1700 Views 8 Replies 5 Participants Last post by  Steve Pituch
Got ingredients from, mixed them with 300ml lukewarm tap water, and there's a layer of silt-like stuff on the bottom and chunks here and there.

How the heck do you get it to dissolve?
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What are the ingredients of this "PMDD" recipe? The "silt-like stuff" is probably impurities from the K2SO4.

If you're worried about dissolving everything or dealing with aqueous solutions, then you should consider dosing dry. It's a bit less accurate but plants/algae aren't that sensitive IME.
Standard Conlin Sears formula:

300 ml tapwater
1 tablespoon chelated trace mix
1 tablespoon MgSO4+7H2O
2 tablespoons K2SO4
1 tablespoon KNO3
S&C's PMDD formula can work for lower light tanks, but is quite difficult to deal with in higher light tanks. What's your tank size and light intensity?
I just want to know how to get it to dissolve better. That's the issue here.
Hot water helps. But I usually have to give it a good shake for atleast a cople of minutes for things to really dissolv.
I wouldn't use hot water because heat destablizes the chelated trace mix. To what extent, I don't really know.

I would just add more water and a little bit of HCl to aid the compounds dissolve. If the silt is indeed impurities, then they may not dissolve completely at all.
Personally, I feel you are better off mixing those elements individually rather than a big mixture of everything. Then you can dose them individually based on test results or plant health. That idea of having a mixture of everything and thinking it will work on any tank has never run well with me. Good for the traces but macros need a little more personalization than that from tank to tank.

Otherwise use twice as much water and double your doses. The more water the easier it is to dissolve everything.

Hope that helps
Giancarlo Podio
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
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