PMDD Paper

      COMMENTS ON "Control of Algae in Planted Aquaria

The initial conditions of Case #1 include a UV sterilizer. That
couldn't have helped your dissolved iron levels. In Case #2 you
installed a carbon filter to the same effect.

"Because others have observed that tanks with CO2 fertilization have
relatively little red algae [5], it tempting to speculate that at
least some red algaes are able to utilize bicarbonate, giving them an
advantage in aquaria where most of the available carbon is in this
form (typically those with high carbonate hardness and high pH)."

"Red algae is favored over green algae if most of the available
carbon is in the form of bicarbonates."

While the red beard/brush algaes seem to take off when my DIY CO2 
runs out, that may simply be due to diminished competition with the
plants. I wouldn't be tempted to conclude the above until I had
better proof. It is a pretty broad generalization and there sure
are a myriad of red algaes. 

Why do you advocate 0.1 ppm iron as opposed to 0.3 ppm?

If you check The Optimum Aquarium page 70, you will notice that of
the cations present in the water, only potassium and sodium are
available in proportionately large amounts. On page 68 mains water
is compared to water in the cryptocorne areas. Note the abundance
of sodium and potassium in the latter. This tells me that, within
reason, one should not be afraid of overdosing with potassium and
that one would be better off substituting KCl for K2SO4 in the PMDD.

I had a similar experience to Case #1 when my experimental 29 gallon
was just set up with the Webb-Kelly RUGF. I had put a pond tab bits
in the substrate and within a few days green-spot algae appeared. It
also seems to favour bright light (I had installed a new MH bulb).
It was eventually replaced by beard algae. Every algae has its

I was a fool for assuming over the years that the 0.8 ppm potassium
and the 2.3 ppm magnesium in the water supply would surely be
adequate. Although I had warned others in an AGA article in 1992
to watch out for potassium deficiency, I have not followed my own
advice until very recently. Reviewing some old hydroponic data that
I'd copied as well as George Booth's recent post of Dupla information,
it appears that quite a lot of potassium is required by aquatic
plants, more than almost any other nutrient, and in greater quantities
than required by terrestrials.

Your hypothesis rings true. I'll suggest two possible reasons for
this. In the wild many of our ornamental aquatic plants grow in
waters of very low nutrient levels. Perhaps, in the case of the
algae, a higher threshhold of phosphorus must be attained before
intake occurs. Growth then takes off. Macrophytes are more adaptable,
complex, the processing takes longer and there may be more inter-
mediate steps, i.e. long term storage, conversion, and retrieval.
If phosphorus levels in the water are very low the ability to store
this element becomes critical. It might explain why my system of ad
hoc additions of hydroponic nutrients every few days has produced
mostly algae. This is what my neighbour has been saying for years.
He has two immaculate planted no-tec tanks. He uses Micronutrient
Mix, no CO2, good filtration and a double fluorescent fixture.
Growth of course is slow but steady. I recently gave him some
K2SO4 since some of his swords appear to be potassium deficient.

The above question must have been addressed many times in the
specialist literature. This is how governments prefer to spend
their research dollars.


About ten days ago I mixed up a batch of PMDD for daily dosing. Three
of four tanks are better, two most noticeably. As you have said it's
the stability of the levels and of the proportions of the nutrients
that is also important. Daily dosing ensures that the plants are always
growing at least marginally and able to use the phosphorus constantly
released by the substrate, by the fish, or by plant decay.

Since switching to PMDD the experimental tank has undergone drastic
change. Previously most of the plants were wearing coats of short,
black, brush algae. The SAEs hadn't a hope in hell of keeping up. I
removed the five ottocinclus and the three SAEs. Seven days later it 
is dying back and being replaced by mostly filamentatious green stuff.
The plants are growing slowly and are probably phosphate-limited. There
are no fish in the tank and lots of light. Next week I plan to add
fifteen white clouds to see what effect their metabolic activity

The best tank is a fifteen gallon with 8 otocinclus and three spawning
rasbora maculata. One week after starting the daily PMDD regimen, all
the plants are doing fine, oxygen bubbles are visible, and there is
only a bit of green spot algae on the lilaeopsis. It is the only tank
which was bleach-treated several months ago. One food tablet and 1 ml
of PMDD enters the aquarium daily.

The third tank, the 180 gallon, is now always well-oxygenated which
had been the case only sporatically before using PMDD. It is lit by
only four 40 watt fluorescent lamps and supplied with DIY CO2. It's
still covered in black brush algae.

The algae in the fourth tank apprears to have stopped growing, but
no retreat is evident yet. The water sprite is growing at a phenomenal
rate and obviously sucking up nutrients.

With respect to blue-green algae I concur with you two. It appears
after the plants stop growing. This has occurred when my CO2 ran out,
when there were no fish to supply nutrients, and when the water was
left for weeks without fish or a water change. The common thread is
water depleted of nutrients. The algae starts to take off as the
plants decay and die back. Interestingly, a small tank that contains
just java moss, no filtration, little light, and gets a pinch of
fishfood has never had blue-green algae. The java moss is always

All in all I think that you guys are dead on. Heartening is your
discovery that algae can be eliminated without predators. Before now
I never believed that phosphate levels were necessarily the culprit.

By the way, I've come to the conclusion that the vermiculite/clay 
substrate and my Webb-Kelly system was a nice try but doesn't win
a ribbon. Some of the crypts like to root in the sandy clay. I
suppose one could discontinue the reverse flow and simply pour
nutrients down the tube and into the plenum, hoping for a very slow
diffusion and playing the guessing game again. This might work well
with non-chelated micronutrients, phosphorus and ammonia on a daily
basis, while adding magnesium and potassium to the water column. It
avoids the mess of cow manure. The vermiculite would act as a buffer
for the cations and the ammonia.

Ten days isn't long. The PMDD technique works better than what I
had been doing. Three months will tell. I'm going to have to invest
in nitrate and phosphate test kits. Any recommendations?

Dave Whittaker                       ac554 at FreeNet_Carleton.CA
Gloucester, Ontario                  dwhitt at magmacom_com