problem maintaining O2 levels

loaches r cool

loaches r cool

Snail Terminator
Feb 15, 2006
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Gahanna, Ohio
tristan.homelinux.net
To date its been a year and a hlf since setting up my 75g planted tank. When I first set it up I had noticed in the morning when I got up, alot of my fish were gasping at the top. I did not know about this forum then. After some quick searching online I decided to shut off my CO2 at night. I didnt notice a large improvement, so after some more surfing, I decided to run a powerhead on a night timer to disturb the surface a bit. This seemed to work out. I sometimes see fish near the top but no gasping like before. I havent had much an issue so I have just ran it like this for some time.

However, after doing my water change yesterday I accidentaly bumped the deflector on the powerhead and the flow wasnt really moving the water surface (the output was basicaly pointing flat out instead of 45 degree upwards). I woke up this mornign to see pretty much all my fish gasping at the top and some didnt didnt make it through the night. :sad: RIP, two Turquoise Rainbows, 1 SAE, and 1 kinda rare Printed Loach (aka Zodiac Loach). Hopefully I wont loose any others from the stress but my Zebra loach and a few others don't look so good, and my Leapord Pleco is very bloated for some reason.

This cant be normal can it? I have heard others that need to use an airstone or powerhead at night... but just bumping the powerhead slightly and I am left with a bunch of dead fish. There has got to be something not right here. At this point I am open to any suggestions since I dont whant this to happen again!
 
My 50 gl. planted tank is run by a canister filter, whose return spray bar is set underwater pointing upwards. This method has given me a balance among water disturbance for gas exchange. I'm not dosing CO2 right now, but I'm considering doing it with this set up.
 
That certainly sounds like the fish were O2 deprived, but why would they only have problems at night? O2 and CO2 concentrations in water are independent of each other, so it wouldn't be because there is more CO2 at night. Could the plants really be photosynthesizing so much during the day that they significantly raise the O2 conc?
 
During the night, plant not only stop photosyntetising (whatever way it's spelled :D ) but also consume oxigen as they breathe. Also, remeber bacterial activity withing the bio filter also consumes oxigen all night long.

It's true that CO2 and 02 levels are independent, but a too high CO2 level can reduce the proportional availability of O2.

That's why it's recommended to shut off the CO2 and/or enhance aireation during the night.,
 
How high are you running your CO2?

You're still turning off your CO2 at night?

Have you checked your other parameters? KH, pH, ammonia?

This doesn't sound right to me: if your whole tank is hanging by the angle of a powerhead something is wrong.
 
I have been leaving the CO2 on all the time since reading here its better that way (more of a ph swing if its off entirely, pluss the couple hour lag to build it back up once the lights are on). The CO2 is currently running at 1 bubble per 3 seconds which I thought was a pretty low amount. I did turn it up slightly (was 1bubble per 4-5sec) since I about doubled the plants a month ago. Also, my CO2 is not as effective as it should be seing how my powerhead I got the line hooked to seems to be slowing down and the bubles are getting bigger and mostly going strait to the top. My diffuser got clogged up an me being lazy just hooked the line to the powerhead. I do have the diffuser soaking in bleach right now but that thing is gummed up pretty bad.

I forgot to mention my water chem... its currently at ph ~6.6-6.8 ammonia and nitrites are 0, nitrates 5-10ppm (although the LFS measured it much higher than what my test kit does), KH = 4*.

I am curious as to what others do? How many ppl here have to use aeration / disrupt the waters surface at night? Or are there several folks that do not have this problem at all? I was under the impression this is common, just my case seems to be severe.
 
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You're CO2 doesn't seem all that especially high. I run mine at least that high and don't see gasping fish.

I tend towards smaller fish, so that might be a difference. I followed your link through and while I didn't find a full stocklist, you do seem to be on the heavy side of the coin and with some larger type fish.

Sorry I can't be more helpful…
 
Since we're probably on the same water supply and are both on a 75g tank I'll give you my setup. It's fairly straight forward. CO2 is on a timer. It comes on a half hour before the first set of lights. I have three sets of lights all on timers. It takes a half hour for them all to kick in. CO2 goes off a half hour before the first light. I have no surface agitation but do maintain good circulation. I use two canister filters and a small powerhead. The CO2 is diffused with a ceramic diffuser and the fine bubbles go into the powerhead and get blasted round the tank with the help of the canister outputs.

I also have a higher bubble count than you and keep a lower pH even though out KH is similar. So, I'm really quite baffled about your problem. As for fish size, I do have small tetras and corys but Daveedka (also from our area) keeps larger fish and he's never mentioned any probs running CO2.
 
Carpguy - As far as stocking I am on the high side, and according to some here way overstocked. But I dont see this as the primary problem as the fish do fine when the lights are on. And I dont beleive its high CO2 levels so much as low O2 levels.
I think I am going to have to just have more surface agitation... and probably get another powerhead to insure if one malfunctions that there is a backup.

reiverix - dont know if it really makes much difference but I am actually in Gahanna and they have thier own water.

I was almost wondering if maybe because my CO2 isnt that high that the plants arent photosynthesizing as much as they should during the day and not makeing enough O2 to get through the night. That was just a hunch which might not be the case at all but I was still wondering.

I am thinking I just need more surface agitation. I had my spray bar pointing relatively downward in my tank to avoid any surface agitation at all as per suggestions here before but maybe now thats not the best idea.
 
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