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Re: PMDD Mix and dosage question

Art Balingit wrote (in rec.aquaria.freshwater.plants) :
[he mentions problems with black and green thread algae]

> I decided to try out the PMDD mix of 1 tbsp potassium nitrate, 2 tbsp
> potassium sulfate, 1 tbsp, magnesium sulfate, and 1 tbsp chelated trace
> element mix on 500ml water.  This is the latest recommedation by K Conlin when
> he stopped using a UV steriliser.  My FE before using the mix was 0.1 mg/l. I
> added 5ml on the first day. On the second day, I did  my 25% water change
> (which I do every 2 weeks), then add 5 ml of PMDD.  After 2 hours, I tested
> FE, and to my surprise, it was 0.5 mg/l.  Now, it appears that I am overdosing
> with the trace element mix, but I need to put 5 ml in order to keep 3-5 mg/l
> of nitrate.  I can adjust the trace element mix, but how would I know if I'm
> overdosing potassium or magnesium?  Is there an indication of potassium and
> magnesium overdosing.  Is it harmful to the plants or fish?

You have a green thread algae in the tank and with that my feeling is
that you may find it difficult to get an optimum balance of enough Fe
for vigorous plant growth while controlling the Fe available to the 
filamentous algae. You could give the plants a big Fe advantage with 
laterite or clay balls added to your substrate. Clay balls can be
enriched by mixing with FTE (fritted trace elements) or micronized
iron which are available in gardening stores.

Try to aim for 0.1 ppm of Fe. You may find it useful to actually
weigh a few teaspoons of CTEM and multiply by the 7% content of iron
to determine the amount of Fe you are adding precisely to the tank. I
suspect that 1 tbs. may be too much CTEM especially since you have
measured 0.5 ppm. I'd try cutting the CTEM to 1/2 tsp. and modify this
amount until you get good growth without excessive algae. You want the
Fe at less than 0.1 ppm as we think this may be more than is actually
required. Keep the nitrates as they are or boost them a little. The
ratio of Mg, K & S to N is ok. If anything, you'll get excess N from
plant food (or soil if used). 

If your tap water is very high in Mg (10 ppm or more)
then you can eliminate or reduce the Epsom salts. If your tap water 
contains little Ca, you'll need that in addition to PMDD. The 
concentrations of K & Mg are not critical as long as they don't get
used up completely. Even high N is not serious until you start to get
BG algae (rare in established tanks). The idea is to have enough 
nutrients that P or Fe are the growth limiting nutrients. 10 ppm are
safe levels to shoot for Mg, K, and NO3 but I wouldn't go much
above those intentionally. There's no benefit and high concentrations
can interfere with other nutrient uptake. 5 ppm may be an acceptable
target for Mg.

I base my dosing estimates upon the amount of water I remove and
replace from my tanks. This ensures that tank concentrations do not 
continue ro rise above the concentration if the dose were added only
to the replacement water. Right now I am doing 25% water changes
each week but could probably stretch this out to 2-3 weeks without
running low on K. I find I need an Fe boost once a week or perhaps
a little sooner. Note that my final tank concentrations are going to
be _much_ lower since they get used up especially if I get the supply
of everything just right.

Neil Frank has described a very similar procedure in TAG 10:2 (the 
latest issue) He quotes (lower?) target concentrations in the tank:
0.5 - 2.5 ppm for Mg, 1-5 ppm for K and 5-25 ppm for NO3. NO3 is
easy to test for with kits from the better stocked aquarium retail
stores. These targets may be better to aim at with lower light
intensities.

He also said that some commercial applications utilize 1 ppm
of incremental concentrations of K and 0.5 ppm Mg (which are based
on weekly additions relative to the TOTAL tank volume). I suspect
that these might be high consumption rates and may indicate high 
growth conditions such as with sunlight or MH lighting. We probably
approximate these conditions in well lit tanks with CO2 injection.
Neil, please correct me if I misunderstand what you have said.
We should probably trade notes.

Steve