Odd neon tetra behavior with CO2

Hello everyone,

This question is about fish, but since it has to do with CO2 injection,
something planted aquarium people are rather familiar with, I figured this
newsgroup was relevant enough. My apologies if you feel this is off-topic.

A few weeks ago I started adding CO2 to my water, and my neon tetra have
been behaving in a way I don't understand. First, I noticed that if I leave
the airpump off for too long the neons have trouble getting enough oxygen.
Or at least that's what it looks like. The breathe really quickly and even
go to the surface when the airpump is off for too long. I'll eventually set
up a timer system that will turn on the air bubbles at night, but for now
I'm doing it by hand. The neons don't seem capable of being comfortable a
full day without air bubbles, which I find annoying (especially since the
other fish look just fine), but it's not their fault, and if they need more
oxygen, then so be it. My CO2 system will simply ne allowed fewer hours per
day of maximum efficiency, that's all. No big deal.

Of course, I understand the lack of oxygen issue. What I don't understand is
why the neons tend to hang right next to the CO2 injection point after a few
hours without air bubbles. The CO2 injector is on the right side of the
aquarium, in the back, behind rocks and a big piece of wood. Normally the
neons don't have any reason to hang there. At least they never did before I
started using CO2. Now, if the neons have oxygen problems when the airpump
is off, why would they hang right next to the CO2 source? It seems to me
that, if anything, the CO2 is more concentrated in that area, and there may
be less oxygen. It doesn't make sense to me.

At one point I thought it might be a pH thing. Neons tend to prefer acidic
water, and more CO2 means a lower pH. However, my overall water pH tends to
be about 6.6-6.8 (due to the CO2 injector), which should be fine for the
neons. And when I took a sample in the CO2 corner and tested it, the result
was the same as for the rest of the water. I don't see why they would prefer
the corner for pH reasons.

So, if the aquarium's pH is just fine for the neons, and if the neons aren't
especially fond of long hours of CO2 injection with no air bubbles, why
would they hang in the back next to the source of their problem? If they
really are more comfortable there, good for them, but it doesn't make sense
to me. I also miss seeing them swimming around in the front, where they used
to hang before I started adding CO2.

One thing that should help in the near futre is an increase in the amount of
light my plants get. I've always known I don't have enough light, but I only
recently realized just how bad the situation is. At the moment, I only have
about 0.6 watts/gallon (a single 25 watt tube for a 40 gallon tank). I
understand 2 or even 3 wpg would be closer to what I need, so it seems I
desperately need to add a few lamps, which I intend to in the next few
weeks. I'm hoping my plants will do a lot better, using more of the injected
CO2 and producing more oxygen. If it happens, the neons should fare much
better. I hope they stop hanging in the back corner then.

Any explanation for my neon tetras' behavior would be appreciated. Thank
you.

Francois

I have the same thing happen with my cardinals. Although the only
other fish in my tank are the SAEs (4). And they dont have any
problems. I just have to make sure the surface skimmer is on cause I
dont have an air pump. Surface skimmer seems to help. Before the
cardinals were dropping like flies. Lost over a dozen of them. Then
again it could be other reasons since my tank is a new set up.

Cheers from Buffalo.

*anyone want some snow?

What's your level of CO2 (ppm)? If I were you, with low light, drop the
level of CO2. FWIW, CO2 and O2 can exist independently of each other in
water, but sounds as if the level you have is too high for the light you
have. In my tank, with CO2, you can actually see the leave bubble O2, which
means the O2 level is supersaturated, and the fish don't have any problems.
Also be aware that there may also be a layer of CO2 on the surface of the
water due to CO2 being heavier than air, which may reduce O2 exchange.

Cheeers,
Poe

"François Arsenault" wrote in message
...

One thing that should help in the near futre is an increase in the amount
of
light my plants get. I've always known I don't have enough light, but I
only
recently realized just how bad the situation is. At the moment, I only
have
about 0.6 watts/gallon (a single 25 watt tube for a 40 gallon tank). I
understand 2 or even 3 wpg would be closer to what I need, so it seems I
desperately need to add a few lamps, which I intend to in the next few
weeks. I'm hoping my plants will do a lot better, using more of the
injected
CO2 and producing more oxygen. If it happens, the neons should fare much
better. I hope they stop hanging in the back corner then.

"Keng" wrote

I have the same thing happen with my cardinals. Although the only
other fish in my tank are the SAEs (4).

I wish I could find SAEs around here. All the pet stores have are flying
foxes and false siamensis, neither species being especially useful in my
case.

I just have to make sure the surface skimmer is on cause I
dont have an air pump. Surface skimmer seems to help.

My Fluval 304 filter breaks the water's surface decently enough. But
apparently it's not quite enough for the neons, assuming the lack of oxygen
is indeed their problem. Right now, with the low amount of light my plants
get, not enough oxygen is produced to compensate for the CO2. I might stop
injecting it util I get more lamps.

Thank you for your reply.

Francois

"Poe Lim" wrote

What's your level of CO2 (ppm)?

I'm afraid I don't have what it takes to measure it. I've no idea how much
CO2 I have. Probably too much. But that's because the plants aren't using
enough of it due to the lighting conditions. I'm using 2 Hagen injectors,
which are supposed to be ok for just about 40 gallons (like my aquarium),
each being good for up to 20 gallons. And one of them is running out of CO2.
If my plants were healthier I don't think it would be too much.

If I were you, with low light, drop the level of CO2.

The more I think about it, the more I think I should stop injecting CO2
until I have more more light. As it is, the plants don't get enough to make
good use of the CO2. The CO2 accumulates, not much used by the plants, and
the plants aren't healthy enough to produce a good amount of oxygen. It's
not surprising that the neons don't like the gas situation.

FWIW, CO2 and O2 can exist independently of each other in
water, but sounds as if the level you have is too high for the light you
have.

I agree. I'll figure out a way to add more light, then I can go back to
injecting CO2. I can't know for sure, but I suspect it will work wonders. A
lot more light and an extra dose of CO2 that the plants can actually use
efficiently. Along with the weekly dose of iron-based fertilizer I add to
the water, the plants should be in vegetable heaven. I'm looking forward to
trying it.

In my tank, with CO2, you can actually see the leave bubble O2, which
means the O2 level is supersaturated, and the fish don't have any
problems.

Strangely, I used to observe that phenomenon in my tank a long time ago, say
two years ago, during the first year. It was a steady stream of tiny little
bubbles coming out of some of the plants and floating to the surface. Unless
it was just a gas leak coming out of damaged leaves, I don't know. Anyway,
my plants were doing great back then, even though the light conditions were
the same. Not sure why they've been having more trouble ever since. It seems
to me that, if anything, I've been taking better care of them over the last
two years. I don't mean the CO2, by the way, as that's a very recent
addition.

Also be aware that there may also be a layer of CO2 on the surface of the
water due to CO2 being heavier than air, which may reduce O2 exchange.

Interesting. I've never thought of that. Makes sense.

In any case, while I understand that there's probably too much CO2 in my
water compared to oyxgen, I still don't know why the neons are hanging in an
area that's may be a bit richer in CO2. And even if it isn't, what is it
about the injectors that they like so much? One would expect the opposite.

Thank you very much for your advice.

Francois