NANFA-- The dissolved oxygen thang

Todd Crail (
Sat, 18 Jan 2003 06:14:13 -0500

So I'm laying trying to remember the name of an exotic invasive plant
(teasel) at 5 in the morning and then I'm all awake. I figured, well, I
might as well get Travis the info he was asking for heh. Maybe even get Jim
his testing for the Trip Report Application :) Then hopefully I can catch
a nap before I have to "get up" for the day.

I don't think this segment of information is going to be appropriate for AC,
however, it is an excellent base for a study that could be done with native
tanks, that would be very useful information. Perhaps this information I'm
going to type right now will inspire others to collect the data. I dunno.
Here's the anecdote and what I learned from it.

My marine fish system consisted of 28, 30 gallon long tanks that were
drilled with bulkheads. They all shared a common 100 gallon sump and were
circulated by a 3/4 hp pool pump. Originally, there was a 200 gallon
acrylic reservoir attached, and an additional 15' on the line back from the
pump. I felt the plumbing was inefficient in design, the return rate too
slow for reef dwelling fish, and this feeling cost me a lot a lot a lot of
money. ;) I picked up Escobal's book "Aquatic Systems Engineering" and I
thought I was just going to be able to stuff the system with fish when I was
all done. Aiye Aiye Aiye.

I took out the reservoir (it was ready to bust at any moment anyway) and
moved the sump into the same area where the system was to take the length
out of the line. I also purchased a mombo protein skimmer that uses beckett
pond injectors for it's air source. Pictures of it can be seen at:

They're listed as "SkimmerX". That's a 55 gallon aquarium next to it. It
was basically a big hoobajoo that looked like I knew what I was doing. If
I'd trusted my ecology senses and not the "humans can do things better than
nature" sentiment... I'd prolly be much further along. But live and learn.

So what happened? Well I changed the plumbing to match what an expert said,
I added the big monster skimmer to inject air and remove dissolved organics
the second they evolved in the water, the flow was increased by 3 times, to
the point that it was topping out the bulkhead returns. Time to bring in a
bunch more fish, eh?

I came back the next morning and half of what I did have was dead. And I'd
had them in for a bit and they were all very well acclimated. Was it the
glue? Did someone dump something in my sump? The shipping mortalities were
all over with, but I have a piscean holocaust going on? Not knowing what
was going on, I did the next logical thing and ordered another box of fish
:( When I took nearly all of them to the dumpster the next morning after
their arrival, I knew something was really goofy.

I moved the few surviving tangs and angelfish, which were breathing in an
awful manner, into the coral system which was 14, 30 longs on a common sump,
but had the advantages of a full living system with all sorts of algaes,
macroalgaes, extra bacteria, etc. Within an hour they were all calm and
eating. Now what is that all about?

I had other stuff to do, so in an effort to save electricity, I turned off
the skimmer and went about my way doing other things... Like for a few weeks
heh. But this was probably the best thing I could do, because it gave me
time to reflect and try different things out.

One thing I noticed was either the pump was cavitating (creating pockets of
air inside the chamber) or the line had a hole in it. Somewhere there was
air coming in, and that would gurgle out from time to time. I was never
able to locate that hole and I took the danged pump apart like 3 times
(which was always a job). This wasn't a big problem, so it seemed... But
later I would observe differently.

Another thing I noticed was on days where it was cooler (it was Sept/Oct)
and not necessary to have the front and back door open, and the heat was on,
fish would breathe harder and turn very washed out color. I would switch in
and out a couple tangs, anthias or angelfish each day to see what would
happen. Door closed for 24 straight hours, health seemed decreased, but not
deadly. So one night, I thought... Hey why don't I turn on the skimmer and
see what happens. My 4 test subjects were good and dead the next morning.
Skimmer is back off.

It was becoming evident that there was an issue in oxygenation, but I
couldn't understand why with all the aggitation going on. That's when I
resigned to spending the $200 wholesale on a digital Dissolved O2 probe.
What I found was amazing.

So I reved everything all up when I got the probe calibrated. I found that
the DO2 would *bounce* all over the place. Saturation is at 11 mg/l in
marine water, a level of 7-9 mg/l is a safe range. In my system, as water
would pass, I would get 6.0, 3.4, 5.4, 2.1, 5.6, 6.7, 3.5, 4.7 and so on in
a 15 second interval. It wouldn't sit still. I thought, well something is
wrong with this probe... So I moved it to the coral system. Locked in real
nice at 7.4. Wow. Took it over to the freshwater system, right and tidy at
6.0. Put it on a system that was curing live rock (huge amounts of organics
which deplete O2). Ready steady at 4.5 All numbers I would expect to see.
Now it was time to play...

Something that I noticed by the fish breathing and coloration was that when
the heating "system" was on, things were much worse. The two blowers for
the building were at each end of the system. They were nasty cantankerous
looking things, and they'd melt your contacts right to your eyes if you
stood in front of them. I added this into the testing.

This was done over the course of a couple days. I should have been
recording data, but with the variability in numbers, I just threw my hands
up and wrote down these observations:

Doors open, heating system off, skimmer off... The control. Fairly stable.
Doors open, heating system on, skimmer off... Less stable.
Doors closed, heating system off, skimmer off... Less stable.
Doors closed, heating system off, skimmer on... Much less stable.
Doors closed, heating system on, skimmer on... Very suppressed and very
Doors closed, heating system on, skimmer on, photoperiod over (4 hours after
lights out).... DEADLY. It would rock between 2.0 - 4.0.

Well, there's my answer. Ugh.

I tried it on the coral system and it would suppress in the dark cycle, but
it seemed the algaes had offered a lot more oxygen to begin with. It didn't
hurt that this system was on a 14 hour photoperiod either, whereas the fish
system lights were on when I was there (8 hours). Fun, fun, fun.

I ran my air intakes on the skimmer outside, and that made a huge
difference. However, being that it was a commercial area and I found a van
backed up with it's exhaust right over the intake one morning, well, that
didn't fly. Yikes! Fortunately, I had turned the skimmer off during some
maintenance and forgot to turn it back on that night. That just about made
me sick seeing that. I really didn't want to open the door.

However, for the home aquarium, I've found an outside airline to be very
effective. Well, that is until the danged city goes by spraying for
mosquitos, which, well, I won't start... At any rate, that's not a fun time
running around pulling in lines. That's the one downside. However, as
another case study, one fella in the area who'd spent hours and hours and
hours online getting advice and opinions and dollars and dollars and dollars
trying to get his fish to live, all he needed to do was put an airline
outside. 1/4" airline tube attached to his skimmer air intake out the
window and his fish were just fine. Man of all the $3.00 solutions, huh?
:) His house was a new house that was like super energy efficient, and he
just didn't have enough O2 to mix into his tank when the heating system was
on, as that recirculates air. He also had a monster skimmer. This has also
solved a lot of online contact's problems too. Pretty interesting stuff.

So enough about this marine aquaria junk. How can we use this? Well, I'd
say we'd be able to more saturate our aquariums in the same manner. The
question is how to do this inexpensively and efficiently? I don't think you
need to spend $200 on a skimmer for your 20 gal darter tank lol. Now that
the tank is at home, and well, I'm at home, I'm gonna play with some designs
I've had in mind. It would be prime to make a hang on the back doodad that
has an unnoticeable, sleek design and just evolves outside air into a
chamber. It will be especially interesting to see what effects this has on
fish coloration at higher temperatures, general health and so on. I'll be
much better about tracking data, and that would be something worthwhile for
AC :)

Okay. I think I'm gonna go back to sleep now. :)

I hope you know that this will go down on your permenant record.
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