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RE: Wet/dry filter
I usually find myself agreeing with you on most things. In others I concede
that there are more than one way to accomplish a given objective. And we
may have differing viewpoints and both still be right.
But unfortunately I am not in concurrence with your theory that nitrates are
not a problem in fresh water. Back in the days of Yore I and many fellow
Yoreans also believed that this was true of salt water. We thought nothing
of 600ppm+ nitrate readings as they did not seem to harm the fish. The
current work being done on reef systems is proving that Nitrates have a
severely detrimental impact on inverts. And I would hazard a guess that they
are not doing any good for the fish either.
It is no doubt correct that low concentrations are less harmful than high
concentrations. And there is a point at which the damage being done is not
apparent. But I believe that it is never the less affecting your fish. I
believe that it is retarding their growth reducing their resistance to
illness and shortening their life spans.
As a case in point, for human beings, it is desirable for a persons
cholesterol to be below 200, their triglycerides to be under 100 and their
blood sugar to be at about 100. Last year when I drove myself to the
hospital my triglycerides were over 3000, my cholesterol was over 1100 and
my blood sugar was over 450. As evidenced by the fact that I am writing
this, I was and remain more or less alive. But had I remained at those
levels for much longer that condition would have most certainly changed.
Just because a fish can tolerate high levels of Nitrate this makes it no
less of a pollutant, nor does it make it desirable.
I also am of the mind that incomplete denitrafication does affect the pH of
the water, especially where it is soft to start with.
As far as plants go I have tested some heavily planted and well lit fresh
water aquariums and found you estimation to be roughly correct, that 100ppm
is about normal even after a relatively long time after a water change. And
at that level the pH was already rapidly declining and inverts were in
trouble. I hasten to add that these tanks were relatively large, had gravel
and were not heavily stocked.
I agree, that given a source of convenient good quality water and the time
to do water changes on a regular basis Nitrates can be kept in check. pH
will be maintained and the effects of improper denitrification can be
reduced. But they will build up eventually if one is only doing small
partial water changes.
Now as to the concept of superoxygenating the water goes: Back in Yore High
School I learned that there is a finite level of oxygen that water can hold
in solution which is almost entirely dependent on its temperature. I believe
that water pressure due to depth also had a minor impact, this is somewhat
irrelevant for purposes of our discussion but I mention it as no doubt
someone else will. Once you reach the 100% level the excess oxygen will
precipitate out. There may be some fish which live in very rapidly moving
streams which may be able to use suspended (not dissolved) oxygen but I
don't know of any killies off hand on that list. I am entirely convinced
that some fish can actually be harmed by dissolved oxygen levels which are
As to your comments that the bacteria "competes for O2" with the fish in a
box filter more so than it does in an external filter, this has me entirely
puzzled. The water enters the filter after the fish have had their use of it
and gets re-oxygenated on the way out. Whether this happens inside or
outside of the tank I can not see the difference. I still tend to think that
a corner filter adds more oxygen than it consumes.
There are many methods of filtration which will eliminate ammonia and
nitrite from the water I have seen most of them.
Wet dry filters
wet dry - power filters
wet dry - canister filters
under gravel filters
And most recently the wonder mud concept (jury is still out on this one)
They all seem to eliminate ammonia and nitrate to one degree or another and
when used within their capabilities they keep these levels very near zero.
With the possible exception of the wonder mud filter none do much for
nitrates or pH stabilization.
As far as increasing oxygen to the water the old fashioned airstone is still
hard to beat in terms of simplicity and cost.
With regards to your experiment with the "unterlicht" concept I have no
doubt that it too will work as it is after all an under gravel filter. I do
have some concerns regarding the algae growth under the filter plate though.
My experience with algae growing on the glass over an extended time tends to
indicate the algae on the glass eventually dies as it is starved by the
algae which grows on top of it and turns brown. This could present a problem
if the dead and dying algae blocks out the light to the new growth. Also a
power failure (although most unlikely on the left coast) could stop the
water flow to the algae and cause a die off which could contaminate the
water. I remember when true algae scrubbers were touted as the final
solution to salt water filtration. I have no idea exactly what went wrong,
but a friend who owned a very large LFS commented that they were expensive,
high maintenance and overall less reliable than would be desirable. By the
frown on his face, I took it to mean that he had either tried it himself or
had customers who had.
Finally I noted in another e-mail you are intending to put a powerhead on
your undergravel filter. Another friend of mine who was truly a very
talented hobbyist and LFS owner had prominently posted a warning in his
store that this was to be avoided at all cost. His printed explanation was
about a page long. In part he claimed that it converted the undergravel
filter from a "biological" filter to a "mechanical" filter and as such
caused packing of the media which now required regular cleaning and caused
clogging of some areas with decaying organic material which could produce
harmful gasses or other chemical reactions. I note that his comments were
directed primarily towards the salt water hobby. In the several years that
I knew this fellow I saw him do some amazing things when it came to fish,
both salt water and fresh. And yes, he kept a few small tanks of killifish
on a shelf behind his counter, which he bred himself for his more
So Wright, at this point in this e-mail I remember that I started out by
saying that I usually agree with you, I'm not sure that we are disagreeing
or just looking at things from different perspectives. Quite frankly, you
are most certainly not wrong, trickle filters are after all proven
technology and most of us have substantial levels of nitrate in most of our
fish tanks. But I keep thinking that the reason that your Henri filtered
tank looks so good is that the Henri filter is generating so much plant
From: owner-killietalk at aka_org [mailto:owner-killietalk at aka_org]On
Behalf Of Wright Huntley
Sent: Wednesday, March 21, 2001 1:22 AM
To: killietalk at aka_org
Subject: Re: Wet/dry filter
> Hi folks,
> I have heard tales of this mythical filter system. I have been using lava
> rock in my box filters for quite some time now. As I understand it the
> porous nature of this material creates anoxic areas in its interior.
> denitrification has been determined by many to be more complete than the
> more traditional aerobic denitrafication. Wet dry and trickle filters have
> been losing favor with salt water enthusiasts. I have seen them referred
> as nitrate factories.
Nitrate isn't a problem in fresh water, and this, unlike salt-water wet-drys
is not intended to be a denitrifying filter. Yes, there's some conversion of
ammonia and nitrite to nitrate, probably, but that is a side benefit. The
objective was to get the oxygen-consuming nitrifying bacteria to do their
work *outside* the tank, so the return water could be oxygen rich.
> No matter how hard I try, I keep thinking that the trickle - lava rock
> filter is working against itself. I have no doubt that it works very
> effectively at eliminating ammonia, nitrite and assorted killi-fry but I
> would need to see some actual figures regarding its effectiveness on
Why? My tanks almost never get to measurable nitrate levels on their own any
more. I have to *add* nitrates to all my planted tanks, regularly! Nitrates
are basically harmless to fresh-water fishes in modest to low
> The very fact that Tetra is bringing out a wet - dry filter tells me just
> how behind the times that this concept is. In a discussion with a Tetra
> rep. he confessed to me that their strongest selling point is their
> integrated heater module, which by the way is not fully adjustable.
> When it comes to lava rock, I'm sold. But when it comes to trickle systems
> am not sure that they are really any better than any other filter system.
> am of course open to changing my mind if someone has data to the contrary.
Well, I've been running one for the better part of a year, now, and I'm
impressed that it does exactly what Henri said it will do. The huge wet
outside surface area effectively reoxygenates the water and keeps the
nitrifying bacteria from competing for it with the fish, as *always* happens
in box and sponge filters!
It doesn't replace water changes. I've never heard that claimed for it.
Nitrates are a toxin in salt tanks, but utterly harmless at <100 ppm in
fresh water. Change some water once in a great while, and that level will
It does seem to improve oxygen content -- a major way to reduce ammonia
It does require more RO topping off, but that is compensated by lower temps
in summer. [Yea! My fishroom was at 84F this afternoon and it's not
Whatever it takes to make a tank have that "sweet and healthy" look, this
tank has it, even when water changes are a bit neglected. I wish I had time
to build about 36 more!
What kind of a sponge do you have over the inlet that it kills killy fry?
I've had really small, newly-hatched *boitoni* in mine with no losses from
the filter that I was ever aware of.
RJ, you gotta try it right alongside a tank with an inside filter to really
appreciate what it does. That's what I've been doing. It will make you a
believer, like it has me.
PS. I have discovered an invisible way to accomplish nearly the same thing
for more "showy" tanks. I have one in my family room with high Oxygen and
happy Lampeyes. :-) [It has no ugly rain-gutter Henri filter sitting on top
Wright Huntley, Fremont CA, USA, 510 494-8679 wright at killi dot net
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