[APD] RE: Dosing 2-3x week vs daily dosing

["Thomas Barr" <tcbiii at earthlink_net>]

> I was wondering if there were any advantages/disadvantages to these
dosing techniques. I don't mean practical considerations like remembering
to dose and that sort of thing but more the biology and chemistry occurring.

No.
Some may wish to claim otherwise but I cannot see any difference and I
would argue from a plant's needs prespective otherwise. There may be some
subtle differences due to someone's routine, but it's not related directly
to dosing frequency with these daily vs 3x a week.
It also depends on light and plant biomass/other issues. 

> With dosing 2-3x week, nutrient levels would be expected to fluctate more
within the desired range than daily dosing. Would this difference have any
influence on 
>plant growth/health or would it make little difference as long as all
nutrients are within the desired range?

Does a plant have to have such a narrow range for good growth? 
Daily vs 2-3x a week really depends on if the plants needs for growth and
maintenance are being met, then either method works similarly. If so, then
it does not matter. 

> Specifically in regards to iron dosing, how long does the iron remain
available for plant uptake once added with such a high oxygen
concentration? 

Well iron disccussion have gone around and around, but I'd certainly
challenge anyone's contention about daily vs 3x a week being "better". 
That's a whole other discussion in itself.

>Is there anyway of knowing?

No, not without serious research methods. The question you are asking is
how much iron is bioavailable to the plant. We add far more iron than any
plant would use, most of it gets bound/oxidized/complexed in the water and
reduced in the substrate etc. 

 >We generally dose way more than could ever be assimilated, right? 

Yes.

>But isn't most of it oxidised to less available forms, hence an iron 
>test kit really gives little useful information? 

Yes.

> If the iron is only available for a relatively short time after dosing
then one possible benefit of dosing every few days might be that if plants
can take up excess iron 
>and store it for later and algae can't, then the plants would do fine
until iron is dosed again whereas the algae may suffer.

You are not going to limit algae with iron. There's just no way you can do
that and have any iron in the substrate or plants that have iron in their
tissues.
Plants leak, they rot, they transport iron up from the substrate and this
leaks out etc. Algae need such ridiculously small amounts you have to be
extremely careful as a researcher to measure Fe limitation in algae. 

> If so, daily dosing would give algae an advantage. Does this make any
sense or am I way off here? Comments would be appreciated.

No, it would not. algae are not having any issue with iron as it is. 

> BTW - I'm currently dosing traces daily, but thinking about trying 2x
week and seeing if it makes any difference. Algae is not to bad, but it's
there. Plants are healthy.

Try 3x a week, if you have moderate light, decent fish load, try 2x aweek,
lower light, you can do once a week.
It's best to have plenty of porous iron rich clay and traces being added to
the water column, not just one of the other.

Dosing the water column will only get you so far before you have to supply
a plant with iron in the substrate.
Plants first reduce iron, take into the cell, chelated it for transport
within the plant. 
This iron can be transported to the growing tips from the roots, but
perhaps most of the iron is used in the lower portion/roots etc when folks
also add the iron to the water column.

Much of the water column dosing supplies the leaves and upper portions. I'm
sure some is supplied to the upper portions of plants from the root zone
but this maybe due having less drain and so call "reversed transport",
transporting iron _backwards_ down into the substrate where it normally is
for many plants that need much more than an alga. There's cost and issues
with transporting iron and other trace metals. Copper is used by the plant
through the same trnasporters appraently. 

You could label the iron with an isotope of iron and see where and how much
went where in the plant and also measure how much an alga used per dose/per
week etc in a planted tank or alone without plants present if you wanted.
I'm doing this now with NH4... and NO3 hopefully. But I'm not sure if I'll
separate the roots from the leaves to see how much went where by plant
organ..but nonetheless, it can be done if you want to answer that question.
Dry the sample and process it for mass spectrophotometery to see how much
went where.
 
Hope this helps.
Some folks use dosing pumps which I'll end up doing at some point. They
will likely be done on a daily routine for simplicity's sake.
Anyone that has not forgot to dose a few times is not telling the truth, I
joke about being lazy, the reason is the
forgetfulness/procrastination/apathy factor.

I try and make it easy as possible on myself while still having a balance
of control and simplicity/cost.
Over engineered systems on 10 different tanks sucks, one single system that
links 10 tanks is not so bad though. That's where I draw the line.   

Regards, 
Tom Barr

> Clint Brearley
> Melbourne, Austalia
>



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