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Re: Oxidization of nutrients

Daniel Larson seems to have worked himself into a state...

"I got a tip that said that high DO-levels might oxidize nutrients so
plants can't use them. In our light-, CO2- and nutrient-maxed
aquariums the DO-level is often higher than the oxygen saturation-
level for water. This ought to be very bad for the nutrients?"

It _can_ be, for some nutrients.

"Browsing the archives I found James Purchase post:

Careful......you're attributing that information to me. While it is true
that I posted it, the information it contains comes from the book "The
Optimum Aquarium" by Dupla and from Allgayer & Teyton, who wrote "Aquarium
Plants". The information I gave on chelators came mainly from Allgayer &
Teyton and is a direct quote from that book. They deserve the credit/blame,
not me.

>>"Recent studies have shown that there are conditions under which the
>>of these critical nutrients can not be achieved from water change to water
>>change, with the necessary continuity."

"(!) Here I got scared because I use(d) the 50%-reset-method with weekly
water changes and weekly nutrient doses."

The quoted material is (I believe) based on the observation that ionic
conditions in the tropical streams they studied were remarkably constant
throughout the year - during both high and low water periods. Nutrient
levels in the streams they studied showed that while the individual
concentrations were low, they were constantly refreshed (as new water flowed
through the stream). If a plant used up all of the nutrients in the water
immediately surrounding it, it wouldn't be long before a fresh supply came
along in the moving water.

In an aquarium that doesn't use a "flow-thru" approach (most don't, its too
wasteful of water), it is the responsibility of the aquarist to ensure that
proper nutrient levels are available at all times. I fail to see why you
would get scared because you change 50% of the water weekly, so long as you
remember to fertilize the new water at appropriate levels. I regularly
"flush" most of my tanks, and the only down-side to it is that you end up
using more fertilizer. But it can correct imbalances relatively easily,
provided that the fresh water you are introducing is O.K.

Dupla was stressing "constant conditions" and were willing to employ lots of
expensive technology to provide that level of consistency (like constant
monitoring of pH to ensure consistent CO2 levels). I don't know how
necessary this is in an aquarium - even in nature, pH fluctuates on a daily

>>"Another better method would be to prepare a daily or a 24 hour
>>like fish food, consisting only of the "critical" nutrients and to ad it

"(!) Which suggest that weekly doses isn't the way to go, or am I
missing something?"

Dupla was referring to providing a consistent level of nutrients like iron,
which can oxidize relatively quickly in an aquarium. Provided the iron (and
other oxidizable metals) is chelated correctly, it ought to stay in solution
for a few days, and thus available to the plants. Dupla's approach is an
effort to stay away from the roller coaster nature of supply and demand if
nutrients are only introduced in large amounts infrequently. Again, with
properly chelated micronutrients, this is probably not so much of an issue
in an aquarium.

""I add every 2-3 days the following: KNO3, PO4 source, and a trace mix(TMG,
SeaChem flourish etc). Weekly I don't get nearly as good results I feel."

I don't think you need to worry about the chelation of nutrients like K+,
NO3-, HPO4--. The TMG you use already HAS a chelating agent in it, which
will keep the micronutrients it contains in an available form for several
days without much problem and while Seachem products don't contain EDTA,
they are formulated with ferrous gluconate which will keep the iron
available for a while.

When you say that you are dosing every couple of days and you "feel" that
you are getting better results than if you only dosed weekly - have you
tried both methods and seen better growth in your tanks using the more
frequent schedule? If you have seen better growth in YOUR tanks using this
method, what are you worried about. You want to learn what works for YOU,
not what works for me or Tom Barr or anyone else. Use other people's advice
as a guide only.

"The reason for my concern about nutrient oxidization is that I dose(d)
weekly and
the results were pretty good, but the last two weeks I have dosed TMG two or
three times every week and the results seems to have improved."

Two weeks isn't long enough to form any sort of valid opinion, one way or
the other. Relax, sit back, continue to do what you are doing, and watch
your tank over several months. Maybe take a series of pictures of your tanks
over that period and then compare them. After about six months you ought to
have a feel for how YOUR tank is reacting.

James Purchase