Argh.... lost one of my Serpae Tetras

[talldutchie]

50/50 what?

The point is that the plants aren't processing co2 and creating oxygen at night. During the day, co2 is absorbed. Bubblers will add constant dissolved O2 throughout the night. The oxygen produced during the day doesn't stay in the tank all day/night, because it's being used by the fish, so it's irrelevant. You need to be concerned with what's happening at the moment. Without dissolved O2 in water, fish cannot breathe.

I think perhaps we misunderstood eachother. I'm trying to understand your point and see if I can help here.

If we simplify things a lot we get CO2 from the fish which the plants take together with some light. They use the C to build cells and return the O2 to the water.
During the night the plants do indeed return some Co2 and don't produce O2 but that's not going to be the same amount as they took during the day otherwise they would not be able to grow.

Now your point that the O2 in the water is used during the night and not supplemented is entirely true.
The point I was trying to make is that a casual reader might get the impression that a densely planted tank means the fish will suffocate during the night. If that was so then the densely planted jungle tanks some people keep would not be able to support life and that's simply not so.

18 fish of serpae tetra size in a 75 gallon is not exactly dense stocking.

So.. my point was that O2 levels during the night might play a role but perhaps there's something else at work here as well.

As to bubblers... I know from the aquascaping crowd that simply producing big bubbles doesn't lead to much gas absorption in the case of Co2. I don't see how that would be different for O2. (and you're not just pumping in pure o2, 4/5 of the bubbles in nitrogen).

Surface agitation, either from a hob filter, a spraybar or even a wavemaker, seems to trap a lot more O2 in the water.
I've tested this in the past. A spraybar slightly over the water level leads to a lot of tiny, tiny bubbles that stay in the water a lot longer than the bigger bubbles created by an airstone and pump.

[Goes to 11!]

As to bubblers... I know from the aquascaping crowd that simply producing big bubbles doesn't lead to much gas absorption in the case of Co2. I don't see how that would be different for O2. (and you're not just pumping in pure o2, 4/5 of the bubbles in nitrogen).

Surface agitation, either from a hob filter, a spraybar or even a wavemaker, seems to trap a lot more O2 in the water.
I've tested this in the past. A spraybar slightly over the water level leads to a lot of tiny, tiny bubbles that stay in the water a lot longer than the bigger bubbles created by an airstone and pump.

+1
I totally agree with this, [& CMs post as well] It is the surface agitation that facilitates gas exchange.

This tank is not overstocked or heavily planted IMO & I have to think that there is something else going on.

[mrramsey]

Would that be a correct assessment?

Is your tank planted? If so, how heavily planted is it?

Yes that is correct. It is not heavily planted by any stretch

From the FTS you showed us i can only see maybe 5 of them in there, and it may have been that he was singled out and picked on to death. If you have more in the school, say 10, it would help to spread out the bickering.
Another thing could be that it was a bad specimen when you bought it. Did you buy them as juveniles or as adults?

Initially I had 7 now down to 5. all of the new ones were juvies, four were added to the group after the tank rescape.

[QUOTE-Dave Waits]I tend to agree with Kevin for what it's worth. Add the bubblers to increase the breaking of the surface-tension and drop the temp a couple of degrees. The Temp drop will allow the water to hold more oxygen to offset the Co2 your plants are dumping at night. Most people tend to run their tank temps a little high. Most of the written stuff cites average water temp where the fish come from and automatically believe the fish will die a horrible death if the temp isn't the same. Most freshwater aquarium fish we buy are many generations removed from that wild place. This is why they tolerate a much wider Ph range,etc. Around 75-76 degrees is about right.[/QUOTE]
I adjusted the temp this morning and lowered to 76F. I can add the bubblers if they are really needed, I already have the equipment for it. I am just not too fond of the look and it always makes a mess of the glass canopy.

The concept behind the bubblers is not the bubbles adding o2 to the water. It is the added surface area. That being said I do have a lot of surface agitation going on already.

Any suggestions there?

@CrazedMichael I would have used a spraybar but the new Renas no longer include the spraybars. I could build one I suppose.

I am happy to report that there were no additional deaths overnight. The lights will be on in about an hour. so I will check out their condition then.

Thank you all for the input.

[KevinVA]

It seems that we mostly agree here. It's true that bubblers don't add a lot of surface agitation (but they can if the pump is turned up and you have a somewhat powerful pump), thus not a lot of dissolved O2, but it produces a steady stream and enough to compensate for any lack of added O2 from plants, especially when fish are not at their most active (at night).

Your point about jungle tanks is well-made, however, if you've taken a look at these tanks, they typically use very small fish, like Neon Tetras, calm fish or they're not heavily stocked at all. There's not a lot of competition going on for oxygen and most O2 that's dissolved in the tank will not be consumed entirely.

If you look at the plant:fish ratio, the plants will certainly out-populate the fish by a good percentage, so the dissolved oxygen being added during the day will probably be sufficient to keep the fish healthy and happy.

The more active the fish, the more oxygen will be used in the tank. Serpaes are very active tetras. About the only time they stop moving and chasing each other around is at night, when they're in energy saving mode. And sometimes they don't even stop then.

I'd like to add that during the time my fish were dying, I had a koralia evolution pump, in addition to a standard filter outlet (not spray bar) from my cascade 1000 cannister filter. It wasn't until later that I switched to a spray bar. It's possible I don't need the bubblers anymore. However the Koralia pump + filter outlet did create quite a lot of surface agitation. Who knows...

I'm glad you didn't see any deaths overnight. Hopefully you don't have anymore, but when this was happening to me, the death rate would drop to every other day. I think I went 2 days without a death once. I had about 7 or so Tetras die at that point, until I could figure out what the problem was. 7 fish in a week or so doesn't just happen... even if they're sick, it would take longer than that - and none of them showed any symptoms (perfect looking specimens). Even the Serpaes that I added to the school from my 10gal (I had 3 healthy, beautiful Serpaes from there - which had lived for months) ended up dying.

Just more food for thought.

[CrazedMichael]

Surface agitation, either from a hob filter, a spraybar or even a wavemaker, seems to trap a lot more O2 in the water.
I've tested this in the past. A spraybar slightly over the water level leads to a lot of tiny, tiny bubbles that stay in the water a lot longer than the bigger bubbles created by an airstone and pump.

Yes, but what i do is have the spray bar just under the water level, and have the little holes pointing ever so slightly upwards, so instead of creating bubbles (as you would get if above water and pointing downwards) it just pushes water around the surface creating ripples. And i just readjust the spraybar accordingly to accomodate for water evaporation. The difference with that method and a bubbler, is i feel that a canister does a better job. The reasoning behind this is that the canister drags water from lower down in the tank (less O2 satuarated water) and returns it to the top thus improving the circulation. Especially if the input and outputs are on either side of the tank.

OP - Very easy to make a spraybar out of PVC and a drill. But you could also try to adjust the tube of the filter output to encourage ripples in the same manner.

Hope you havent had any mroe deaths. I like Sepae Tetras i have a large school myself and they are fun to watch.

[talldutchie]

The points Kevin and Michael have made make me want to do a proper test. See if I can figure out a way to measure dissolved o2.

[KevinVA]

Yes, but what i do is have the spray bar just under the water level, and have the little holes pointing ever so slightly upwards, so instead of creating bubbles (as you would get if above water and pointing downwards) it just pushes water around the surface creating ripples.

I do the same thing with my spray bar. This provides even distribution through the tank, as well.

The points Kevin and Michael have made make me want to do a proper test. See if I can figure out a way to measure dissolved o2.

That would be interesting. Not sure it's worth a $22 test, though. However, if you feel inclined: http://www.amazon.com/Salifert-Disso...d+oxygen+meter

[mrramsey]

OP - Very easy to make a spraybar out of PVC and a drill. But you could also try to adjust the tube of the filter output to encourage ripples in the same manner.

Hope you havent had any mroe deaths. I like Sepae Tetras i have a large school myself and they are fun to watch.

None so far! as you can see there is plenty of surface agitation going on.
Any more and I will have white caps