PMDD ? - Tropical Fish Keeping - Aquarium fish care and resources
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post #1 of 16 Old 03-18-2007, 01:51 PM Thread Starter
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Does anyone know how to dose the PMDD? I bought some off of Greg Watsons site and I have no idea how to dose it. Do I need to mix it with water first and if so how much mix to how much water? Or can I just add it dry to the aquarium and if so how much?
I have a 90 gallon that has quite a few plants in it.
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post #2 of 16 Old 03-25-2007, 07:03 AM
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ive read about this stuff. if its the same stuff, i think you should be dosing about a mL... id advise against doing ituntil someone who knows better replies

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post #3 of 16 Old 03-26-2007, 07:25 PM
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I don't know the dosing of the PMDD, I bought the fertilizers separate so I could control them better. I can tell you this, I dose 1/4 tsp KNO3 3x a week in a 10 gallon with no problems.

I would think, and this is only a guess, that dosing 1 teaspoon every other day, 3x a week would be plenty to start with. Watch your growth rates and see what happens. If you don't see much of an effect, add 1/4 teaspoon to the dosing regiment and wait to see. Give it a good 2 weeks after each change in dosing to see if there is a noticeable change and test you levels to make sure they aren't too much.

I will try to find someone who uses them premixed that can help a little more. And yes you put the ferts in a cup of tank water before adding to the tank so they have a chance to dissolve. For a full teaspoon, I would say use a quart jar full of tank water so it can mostly dissolve before adding it to the tank.
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post #4 of 16 Old 03-26-2007, 09:31 PM
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The plant fertilizer I have is 1 cap per 30 gal once a week. I just pour the cap directly into the water. My 90g has pretty good circulation so it doesn't sit very long.
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post #5 of 16 Old 04-08-2007, 09:02 PM
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I wrote to them for instructions and here's the reply I got:

"The reason that we don't make it that simple is that fertilizing a tank properly is that it is simply not that simple. To even start to tell you how much to dose would require additional information, such as your plant load, types of plants, watts of light/per gallon, frequency of water changes and amount per change, fish load, and amount that you feed your fish.

I can tell you to make a solution using a tablespoon of PMDD to 1 liter of water.

The estimate of 180,000 gallons usage is based on two drop of solution per ten gallons per day. But this dosing recommendation does not take into account existing nitrate levels prior to dosing. It may be that one drop per day would be fine, and two drops/day would, under your tanks conditions of light, fish load, feeding, and water changes, result in excess nitrates and therefore an algae bloom.

The simplest way to dose is the EC method described on Under this method you overdose with fertilizer and then change the water 50% per week. There are many strategies that you can try. You will need to find the right one for you and your tanks.

This is why we don't provide dosing guidelines.

You would have the same issues with store bought fertilizers; the
issues are just cheaper with us. Most devoted planted aquarists don't buy PMDD, but instead buy the ingredients of the mix so that they can adjust the ratios to match each of their tank's conditions. But people keep insisting that they want the PMDD, so we keep providing it.

Good Luck, and I am sorry if this answer doesn't provide the answer you wanted."

So all that said, the way we're doing it so far (but only a few days yet) is to mix 1 tablespoon of powder mix to 1 liter of water - then put one drop per 10 gallons of water for lightly planted tanks, and 2 drops per 10 gallons for medium to heavy planting. Hope this helps someone!
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post #6 of 16 Old 04-08-2007, 10:22 PM
I'm glad you posted their reply. I have quite a few planted aquariums, and after reading what they told you, I won't buy any of their product. Thank you.
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post #7 of 16 Old 04-08-2007, 10:24 PM
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Mind if I ask why - because if I'm using a bad product, hubby will be very unhappy about his plants! I read good things about the product, so I thought it was a good choice. So elaborate please??
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post #8 of 16 Old 04-08-2007, 10:49 PM
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It isn't a bad product, just not the best to be able to dose precise needs.

Let me put it this way; You get 10 bags of jelly beans, all different flavors but they are all the same size and color. Put all the jelly beans in one big bag and shake them up. Now reach in the bag and take a big handful. How many of each kind do you have? You really don't know because you can't tell them apart.

The same goes with the PMDD; all of the nutrients that you need are there but you have them all mixed together and can't be sure how much you are actually putting in at any one time of any given nutrient in your solution. You might have a majority of PO4 in there and not enough NO3, The next time you might have a ton of calcium and magnesium but nearly nothing of PO4 or NO3. So on and so forth. I think you get the idea.

Dose the way it says to but I would do the 2 drops every other day because you don't want to dose your PMDD at the same time you dose your Iron. I guess you could dose the PMDD in the morning then 4-6 hours later dose the iron supplement if you want. PO4 will precipitate out iron in solution to an unusable form so the plants will not be able to use it. It is a controversial topic but I have actually seen it happen.

Just make sure to mix up the powder really well every time you make the solution and you should be dosing pretty close to what your plants need overall.

Next time I would recommend buying them individually so you can dose what you need without the guessing game. I do know those that use it and it was used a lot for a long time. It will work you just have to watch for deficiences and up your dosing a little to compensate.

And remember, if you do a 50% water weekly, the absolute highest reading you can have in your tank rom dosing is 2x what you dose. I actually dose 30ppm of NO3 a week with a 50% water change the absolute maximum I could ever have is 60ppm if my plants used nothing at all. This has never happened and I actually maintain about 20-30ppm weekly.

If you give me the PMDD amounts of each kind of fertilizer per pound I can try to get you a general idea of how much you are actually dosing. Well as close as can be done with the mixture anyway.
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post #9 of 16 Old 04-08-2007, 10:51 PM
I don't think that I would purchase a product where the manufacturer could not provide me with a dosage to administer the product. I,too, have read that PMDD is a good product. But, to have to experiment in order to find the correct dosage is a little much. Their claim that all over the counter ferts would have the same scheme of application is a bit left of center. I have to maintain a fair amount of aquariums, many planted. I prefer to use something safe, adequate, and user friendly. PMDD does not sound like it lends itself to being very user friendly and I would have to question the safety aspect as well. What happens if one were to overdose while "experimenting" to find the correct dosage? The manufacturer is avoiding the responsibility of giving adequate dosage and placing that responsibilty onto the consumer(you). I just do not think that is a good practice.
Some hobbyists take special pride in the care that they provide their tanks. And that's good. Then there are those that throw fish and plants into a bowl of water and leave it at that, that's bad. Then , there are those of us that are somewhere in the middle. I like to have time to enjoy my fish, plants,and general biotopes without having myself elbow deep in water, mixing ferts or meds, or constantly rearranging the layout of the tank bottom. The reason I prefer to use user friendly products is that it does give some extra time to enjoy just looking.
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post #10 of 16 Old 04-08-2007, 11:09 PM
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Originally Posted by fish_4_all
If you give me the PMDD amounts of each kind of fertilizer per pound I can try to get you a general idea of how much you are actually dosing. Well as close as can be done with the mixture anyway.
Well everything you both said makes perfectly good sense, but saddens me because I now have so darn much of the stuff now :(

Well here's what's on the bag (one pound bag):
Sears Cinlin PMDD formula
1 tbl Plantex CSM
1 tbl MgSO4+7H2O
1 tbl K2SO4
1 tbl KNO3

I wish I could provide more info than this. I don't supplement with iron though so your "staggered" feeding won't help me. I thought this had everything I needed :(
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