Overnight Aeration

[JLW]

Over the past week or so, I've been having one or two fish per day die in my main tank. They're all fine (those that are within the 1/2" of the glass I can see. , but I find them dead in the morning. The lights come on earlier than I wake up.

I've come to suspect that it may be low oxygen. The lights come on earlier than I'm up, so I don't witness fish gasping at the surface in the morning. But, the tank is very heavily planted, and ... well, it's my best guess.

I've hooked a timer up to an air pump, and am aerating the tank overnight, from about 11 PM to 4 AM. The tank lights go off at 1030ish and come back on at 530 (I get up at 6). They then go back off at 8, and come back on at 4 PM until 1030 again.

My questions are this:

1. With the second "dark" period from 8-4, is this doing anything? The tank does get SOME ambient light, but should I be aerating here, too.
2. Am I going to negatively effect plant growth? I hardly ever actually use the CO2, but it's only ever on when the lights are, and when I remember.


I'm planning on running it like this through next tuesday or so (about 2 weeks), and just seeing if it solves the problem. If I continue to have losses, I'll have to explore further and see what's going on.

J.

[Cristy Keister]

Why don't you shift the morning timer 1/2 hr so you can see the fish before lights on?

[JLW]

It's hard to reach. Plus, I'm concerned I'd lose fish in the meantime, and uh ... these sound like pretty weak excuses.

[150EH]

I think consistancy is important to some degree in a planted tank so a timer with even a low amount of CO2 on a regular basis would be better and it seems your mid-day black out is too long IMO but I don't think either of these has anything to do with your fish deaths unless you are just cranking on the CO2 at a level that is way too high.

I'll have to say I'm a little confuses and not sure I fully understand what exactly is happening or why but you need to make changes in the amount of CO2 and forget about the aeration at night or at midday if your gassing the livestock with high levels of CO2.

[JLW]

I don't think I'm gassing with CO2. I think that overnight, when the plants' respiration rate is much higher than their photosynthesis rate (which would be nonexistent at night), I'm getting borderline lethal levels of oxygen, which are killing fish.

[Cristy Keister]

I don't get that. We all have tanks packed (and not) with plants here, but it doesn't cause asphyxia to our fish.

[scientist0724]

Is it that tank we saw at tank tours that was short and packed with plants?

Have you checked your CO2 tank levels? Maybe you're about to have a CO2 dump?

Arlene

[150EH]

Ok, now I understand but I don't see how that could happen, but I'm not even close to being an expert.

[Sonny Disposition]

Hmmmm.... I don't see a down side to aerating during lights out, as long as you shut the air off an hour or two before lights on, to give the CO2 levels a chance to build up in time for lights on. Plants can't absorb CO2 in the dark, can they? And they're consuming oxygen. So I would think that aerating in the dark would be beneficial for your fish _and_ your plants.

This is how my big (and only) show tank works. I have a powerhead with a bubble making attachment on a timer, which comes on about an hour before lights out (so I can see it and make sure it came on like it was supposed to) and goes off about 90 minutes before lights on, to give CO2 levels a chance to come back up before the lights come on.

I'm getting good growth-- not as good as with injected CO2 get, but the Amazon sword and Limnophilia aromatica are growing. (Per the Walstad book, I also have a two hour lights off from noon to 2 p.m., to give CO2 time to accumulate mid day.

[JLW]

My feeling is that it can drive off CO2 overnight and increase your CO2 expenses, but ohterwise, it can't do any harm.