Oxidization of nutrients

["Daniel Larsson" <defdac at hotmail_com>]

Warning. Messy post follows.

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?

Browsing the archives I found James Purchase post:
http://fins.actwin.com/aquatic-plants/month.200109/msg00092.html

"Earlier we mentioned that iron, manganese and several other trace elements
are only water soluable for a short time. They oxidize in the presence of
oxygen, precipitate and are useless as plant nutrition."

"A good fertilizer will take on this responsibility in the aquarium as well,
by means of a chemical trick.There are chemical substances that bind and
protect certain elements so well that oxygen can not touch them and
precipitation can be largely avoided. These substances are known as
chelators or chelates."

"Recent studies have shown that there are conditions under which the supply
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.

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

(!) Which suggest that weekly doses isn't the way to go, or am I
missing something?
To low DO-level = bacteria can't convert ammonia/nitrite to nitrate
resulting in algae.
To high DO-level = nutrients get oxidized?
Is this the reason you, Tom, dose every 2-3 days?

"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."

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. Same amount
of fertilizer - better results.