Help! DIY CO2 system o/d; fish still dying 24hrs later

[Nimbus]

I've just had a bit of a disaster in my aquarium. Yesterday evening I finally got my DIY yeast-based CO2 system working, and so I hooked it up to a diffuser mounted under a powerhead and left it for a few hours while I had dinner and watched a movie. I checked it when the movie finished, to discover that it had apparently overdosed the CO2 into the tank - a number of fish had died, the others were gasping at the surface, and the water was a bit cloudy. Yikes! I immediately yanked out the CO2 hose, removed the casualties and did a major water change. An hour or so later it looked like things were starting to settle down, so I went to bed.

I woke up this morning to discover that a bunch more fish had died overnight, including several highly valued ones. I did another major water change, and have been doing periodic water tests throughout the day trying to work out what happened. My best guess is that my water hardness was too low when I put the CO2 line in, and as a result the amount of CO2 that the DIY system output was too much for the tank. So I put a bit of KH-increaser in to bring it up to around 5-6 DH, and it's stayed there (more or less) all day as the water has slowly clarified again.

The problem is that I'm still losing fish. The water parameters test ok - this afternoon, pH was 7.0, KH was around 6. By my calculations, that should put the CO2 level smack bang in the the acceptable range, at around 20ppm. Right? But every few hours, another one of my fish (and it's always my precious and hard-to-get honey blue-eyes) starts swimming unsteadily and panting, and then a while later it's dead. I've lost half of them today, and I'm afraid that when I get up tomorrow morning the rest of them will be dead as well. I've put them into a little floating fry-container to keep them near the surface, but that doesn't seem to help. I don't know what else to do. Help!

Some more data re my setup:
Tank: 5' long, 210litres/56gallons
Filtration: Eheim 2215 canister filter, plus internal filter with powerhead for extra circulation
Light: 3x40w 4' 6700k fluorescent tubes

[Gatekeeper]

I am finding it very hard to believe that a DIY CO2 overdosed a 56 gallon tank. You sure this mixture didn't suck up into the tank?

And instead of messing with the water parameters with chemicals, lower the water level so your outflow splashes into the tank (create turbulence), and if so, add a coupld airstones (to get O2 levels up).

[Nimbus]

Thanks for your quick response.

Originally Posted by gmccreedy

I am finding it very hard to believe that a DIY CO2 overdosed a 56 gallon tank. You sure this mixture didn't suck up into the tank?

Quite positive. I have a check valve on the CO2 line between the bottle and the tank.

There was one episode earlier yesterday where a small amount of the yeast mixture from the bottle splashed out onto the lid of the tank. If any got into the aquarium it would have been no more than a drop or so, quite literally. I can't imagine that'd be enough to cause this sort of damage, though. Right? I did note last night when I found all the expired fish that the KH was a bit low - around 3, and the pH was high - I don't recall the exact figure, I was in a panic changing the water and forgot to write it down. But it certainly gave a "way too high" reading on the CO2 level chart. So it seems to me that was most likely the culprit. FWIW, I was getting a couple of bubbles per second from the CO2 bottle at that point.

And instead of messing with the water parameters with chemicals, lower the water level so your outflow splashes into the tank (create turbulence), and if so, add a coupld airstones (to get O2 levels up).

Well, I moved the spraybar outlet from the filter up so that it was providing quite a bit of turbulence, and also adjusted the angle of the powerhead so that it was doing the same at the other end of the tank. I also removed the glass tank covers to facilitate air circulation. That's how it's been all day. At this point, my estimation of the CO2 level based on the current tank pH and KH is "well in the green", and has been so for most of the day. *perplexed expression*

[lovingHDTV]

How big is your DIY system? I have a 46 gallon tank with 4 liters of DIY and can never get enough CO2 into the tank. Which is the norm with DIY.

[Nimbus]

Originally Posted by lovingHDTV

How big is your DIY system? I have a 46 gallon tank with 4 liters of DIY and can never get enough CO2 into the tank. Which is the norm with DIY.

It's based on a 2 litre coke bottle. The mix in the bottle is 2 cups sugar, 6 tsp gelatin, .25 tsp carb soda, and a bit under 2 litres of water. I've been sitting the bottle on top of the light enclosure so that the warmth from the light would encourage the yeast.

I've seen stuff on the net where folk talk about aiming to get a bubble every second or two; my little system's quite consistently producing a bubble every 0.5 - 0.75 sec or so, and has been doing so for a couple of days quite steadily.

Does that tell you anything useful, or give any pointers re what might be worth investigating or trying next?

[Gatekeeper]

Check valve is going to do nothing. If installed correctly, all that prevents is tank water from going back into mixture. It won't prevent the mixture from getting into the tank (or else the gas wouldn't be able to get there )

Not sure if a "drop" would do anything, and to be honest this doesn't sound right....

KH was a bit low - around 3, and the pH was high

kH dropping off, would mean that you would have a volatile pH suceptable to big swings (which could kill fish), but a high pH is unlikely.

I still think that something else is going on here. This just doesn't make sense that a DIY Co2 would reek this much havoc on a tank that size (and even in that short of a period of time).

the water was a bit cloudy

I am still suspecting tank contamintion in some way or something coincident happened.

OR... how old is the tank out of curiosity? is it cycled?

[lovingHDTV]

Do you have a gas separator like shown here?

http://www.qsl.net/w2wdx/aquaria/diyco2.html

I find that mine gets liquid in it, that would have been blown into the tank had it not been there.

(Its the little .5 liter bottle)

[Nimbus]

Originally Posted by gmccreedy

Check valve is going to do nothing. If installed correctly, all that prevents is tank water from going back into mixture. It won't prevent the mixture from getting into the tank (or else the gas wouldn't be able to get there )

Gotcha. That makes sense, yes. I'm still pretty confident that the contents of the bottle did not siphon into the tank somehow - given the bottle was mounted *above* the tank, and every single time I checked it there was a positive flow of CO2 into the tank, I don't see how that could have happened. Could I be missing something there?

Not sure if a "drop" would do anything, and to be honest this doesn't sound right....

"Doesn't sound right" how, exactly?

The amount that spilled out of the bottle onto the tank lid probably wouldn't have been more than around 10ml, max, at a guess. What happened was that I took the cap off and (foolishly) attempted to top up the water in the bottle; this caused the contents to foam and a bit of foam to spill up and out onto the tank. I mopped virtually all of it up off the glass lid with an absorbent cloth; a little dribbled down the outside front of the tank. I checked the edges of the lid to see if any seemed have run into the tank; I didn't see any but I mopped it with the cloth just in case. So it's possible that a small amount might have got in, but I don't think it'd be more than a few drops if any. Does that sound like it might be a possible culprit, do you think?

kH dropping off, would mean that you would have a volatile pH suceptable to big swings (which could kill fish), but a high pH is unlikely.

I'm sure you have more experience with this stuff than me (not hard!) so you're probably right. Perhaps you can explain to me exactly *why* a high pH is unlikely, under the circumstances? Given that pH, KH and CO2 are tightly coupled, if the CO2 is high for a given KH, wouldn't that lead automatically to a high pH? Or have I misunderstood how this works?

I still think that something else is going on here. This just doesn't make sense that a DIY Co2 would reek this much havoc on a tank that size (and even in that short of a period of time).

Yes, it did all seem to happen very quickly. I've been keeping aquariums for twenty-odd years, and I've never seen anything like it. But then, this is the first time I've tried a CO2 system of any kind. *shrug*

I am still suspecting tank contamintion in some way or something coincident happened.

OR... how old is the tank out of curiosity? is it cycled?

Oh, it's well and truly cycled. :-7 It's been running in its current position since 1994. One of the fish that died yesterday was a 10-year-old clown loach.

The only *new* things that could have affected the tank in the last couple of days are things related to the CO2 setup. Everything else is as it has been for quite some time. Nothing other than a splash of yeast mixture has been spilled on the tank, no new chemicals (apart from CO2-related stuff) have been introduced. The cat hasn't puked in the tank. Honestly, everything else is as per normal.

[Nimbus]

Originally Posted by lovingHDTV

Do you have a gas separator like shown here?

http://www.qsl.net/w2wdx/aquaria/diyco2.html

I find that mine gets liquid in it, that would have been blown into the tank had it not been there.

(Its the little .5 liter bottle)

Interesting! No, I haven't got one of those on my current setup. I think that CO2 System Mk II (if I can find the nerve to try it again after the recent disaster) will definitely include one - it looks like a useful refinement. Thanks for the tip!

It's probably worth mentioning that the diffuser that I had at the "wet end" of the CO2 line was one of those little inverted-bell-shaped ones with a ceramic disc in to diffuse the gas through. I'd imagine that anything chunkier than gas would wind up sitting in the little u-bend at the bottom of the diffuser rather than passing into the tank water. Looking at the diffuser now, the water in it is crystal clear - no sign of contamination visible, at least.

[tazcrash69]

I would honsetly, do a couple large water changes, let everything stabilize, then try again after a few days.

I have to agree something contaminated the water, but even 2 BPS in a 56 shouldn't do it.

Also, you said "a little less than 2 liters of water" in a 2 liter bottle. I used to fill to where the bottle curves to avoid getting the yeast slurry in the lines.

[Nimbus]

Originally Posted by tazcrash69

I would honsetly, do a couple large water changes, let everything stabilize, then try again after a few days.

Lacking any other great plan at this point, that's pretty much what I'm thinking, too. I just wish I knew why my honey blue-eyes are still going belly-up, one at a time. Is it preventable? I wish I knew...

I have to agree something contaminated the water, but even 2 BPS in a 56 shouldn't do it.

What is "BPS"? I don't think I've met that abbreviation.

Also, you said "a little less than 2 liters of water" in a 2 liter bottle. I used to fill to where the bottle curves to avoid getting the yeast slurry in the lines.

That's where I had it originally, but then I started getting concerned that I might have left a bit too much headroom in the bottle, and wondered if maybe topping it up a little, so that the water's about halfway up the curve, might be better. That's when I had that Escaping Foam Incident that I mentioned upthread. :-\

[tazcrash69]

BPS is bubbles per second (a very rough gauge of CO2) like WPG watts per gallon.

Personally I think the slurry getting in the tank is what probably did it.
A bacterial bloom can rob an aquarium of oxygen.

In the case of the extra space, just give the yeast a litlle time. they will make enough.

In the mean time change lots of water, and some surface motion to promote gas exchange.

[Nimbus]

Originally Posted by tazcrash69

BPS is bubbles per second (a very rough gauge of CO2) like WPG watts per gallon.

Personally I think the slurry getting in the tank is what probably did it.
A bacterial bloom can rob an aquarium of oxygen.

In the case of the extra space, just give the yeast a litlle time. they will make enough.

In the mean time change lots of water, and some surface motion to promote gas exchange.

OK then, since it seems to be the consensus that the CO2 itself is unlikely to have caused my problem, I've put the CO2 line back into the tank, and will be watching very closely for the next little while to see what happens. Wish me luck! (And thanks for all the responses, folks!)

[tominator]

Originally Posted by Nimbus

Gotcha. That makes sense, yes. I'm still pretty confident that the contents of the bottle did not siphon into the tank somehow - given the bottle was mounted *above* the tank, and every single time I checked it there was a positive flow of CO2 into the tank, I don't see how that could have happened. Could I be missing something there?

Sorry, this is an older thread but if I am reading this correctly than your 2L bottle is above the tank. I believe that this would allow the mix in the bottle to siphon into your tank, it goes from high to low position, thus when you do a water change you put the end of the syphon tube below and not above the tank. As mentioned earlier a check valve won't do anything for keeping the mix out of the tank, but will keep the tank water out of the mix. If you do have a check valve it's probably best to put the bottle below the tank and the check valve will keep the tank water out of the bottle and gravity will keep the co2 mix out of your aquarium.

[Nimbus]

Thanks for the feedback! Having dealt with the yeast bloom (and sadly lost half of my fish because of it), I've rebuild my co2 setup as folk have suggested here -I've added a separator bottle and relocated the whole lot to under the aquarium. So far it seems to be behaving itself...