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Re: HCl vs. HNO3. RO/DI and electrolytes. Role of oxygen

Bjorn Straube wrote, June 23:

>Subject: HCl vs. HNO3

>I have been keeping my PMDD in the frig and decided that I have gotten
>tired of walking back and forth between it and the tank (yes, I know I'm
>lazy..."work smarter not harder" ;) ).  The acids I have handy are
>hydrocloric, nitric, phosphoric, and sulfuric.  The formula for PMDD
>calls for HCl but I figure why not add the the nitrogen instead of
>clorine?  Anyone see a problem with that?
One possible problem is that HNO3 is a fairly strong oxidizer, and the
chelating agent for your iron may be susceptible.  I am not enough of a
chemist to know for sure.  It might be safer to add the nitrate to your
tank separately.

Ric Cooney wrote, June 23:

>Subject: RO/DI and electrolytes

>....Some time ago I seem to recall a discussion about the use of RO/DI
>units   >and the need to reintroduce electrolytes such as RO Right to
>allow fish to live >in this "pure" water. If I remember correctly the
>conclusion had something to >do with osmotic balance and gill function.
>Can anyone lead me right???
Fish have mechanisms to take up sodium, chloride, potassium, calcium,
possibly magnesium, and probably some other ions.  In order to maintain
proper internal concentrations of these and other ions, they must have
minimum concentrations in their water.  These concentrations can be quite
low for many freshwater fish, but they can't be zero.  Fish have active
transport mechanisms for uptake primarily in their gills.  They have
impermeable skins to help reduce the rate of loss.  (I am just going from
general knowledge here; there may be a lot of specific research in these
areas the news of which has not got as far as Tougaloo College.)

Michael Eckardt wrote June 23:
>Subject: the role oxygen in a planted tank
>Kasselmann (Aquarienpflanzen) and Horst (Pflanzen im Aquarium) discuss the
>role of oxygen in a planted aquarium, yet I have not seen any references to
>the subject here on the APD. Both suggest that a high, constant O2 level is
>beneficial to the plants as well as the fish and the bacteria and results
>in a healthier tank.
>Apparently, the plant growth was higher in an (artificially) oxygenated
>aquarium than in an identical, non-oxygenated setup. No reasons were given
>(Kasselmann). Also, Horst says that one of the most important functions of
>a trickle filter is its ability to saturate the water with oxygen, to
>maintain a conststant O2 level throughout the light and dark periods.
>Again, he suggests that O2 plays an important role in plant growth. Why?
>And now to the questions:
>Do plants suffer at night when the O2 drops?

They shouldn't suffer unless the oxygen content of the water drops
considerably below the equilibrium value with air.  During the night the
roots are supplied by oxygen diffusing into the plants' air channels in
leaves and stems and then diffusing down into their roots through the air
channels.  Oxygen diffuses something like 100,000 times faster through air
that it does through water.  If the content in the water is near the
equilibrium value with air, the roots can be supplied indefinitely, even in
the absence of light and the process of photosynthesis.

>Are the plants'  resources being used up to rebuild the O2 level in the

I don't think so.  They just start photosynthesizing when they are in
light, and oxygen is a byproduct of the process.  Photosynthesis produces
sugars, which can then be rebuilt into all the ogranic molecules needed by
the plant, assuming that it is getting all of its essential mineral

I noticed also that section in Kasselmann on the importance of oxygen and,
while I havn't read it carefully (That takes me a lot of time :-)), I
wondered why the emphasis.  I know that if something is decaying in the
water and seriously lowering the oxygen content the plants can die off
rapidly and completely.  However, under normal conditions where, say, fish
don't need to come to the surface, I don't think there would be much damage
to plants.

>Should I look at trickle filters or H2O2-oxygenators?

Actually, during the day in a non-mechanically filtered tank the water can
become supersaturated with oxygen coming from the plants.  Mechanical
filtration during the day could actually lower daytime levels, although it
would probably raise nighttime levels a little.  I think I would have to be
shown research results that indicate considerable improvement in growth
rates due to nighttime aeration.  The negative of nighttime aeartion is
that it would flush out a lot of CO2 that you may have gone to considerable
effort to introduce.

By the way, in the research mentioned by Kasselmann, I wonder if they took
into account that the plant growth in the aerated tank might be due to
greater water movement past the plants rather than  more oxygen in the
water.  Greater water movement could allow more efficient nutrient uptake.
In order to control for this the water would have to be circulated in the
unoxygenated tank at the same speed as in the oxygenated tank without any
extra oxygen uptake due to water movement---a difficult sounding task.

Paul Krombholz                  Tougaloo College, Tougaloo, MS  39174, in
steamy Jackson, Mississippi where we got up to 91 degrees F. yesterday and
are forecast to get to 94 degrees today. Summer is here.