Sudden pH Change Due to ...Water Movement?

[justin.sterling.scott]

I'm confused about what happened last night. I'll attempt to keep it concise.

60 gallon corner bowfront; gear in back corner; cannister intake on right, outlet on left, heaters between (which makes no sense, really). Recent reading has placed water movement concerns in my mind. Currently, my mental state is reverting to paranoid newbie (research, inquiries, testing, daily tweaking, more research...).

5:00 p.m. - Just home from work, found an angelfish corpse. Concerned for the safety of other fish due to lack of oxygen, in turn due to lack of surface movement, I turned on the four inch bubbler in the back corner which usually switches on when the lights switch off.

8:00 p.m. - Home from kid's band concert, lights still on, bubbler still on.

8:30 p.m. - Lights turn off as I'm preparing to test basic water parameters. Pulled a water sample from front of tank and tested pH, ammonia, nitrite, nitrate. pH color chart suggested ~6.4, which is the lowest reading I've had since tank startup (~45 days ago). Ammonia, nitrite, and nitrate levels sat'; prepared to do weekly water change following day.

8:40 p.m. - Turned lights back on. Added powerhead to tank; placed on left, directly below cannister outlet; powerhead outlet about two inches above gravel, pointed at front left corner, askew with cannister outlet flow. Observed water movement via plant leaves, fish, and stirred detritus. Found swifter, sat' movement along radius of front glass to opposite/intake/right side of tank. Found slower, sat' movement in center of tank.

8:50 p.m. - Pulled water sample from tank. pH color chart suggests ~7.6. Pulled another sample and tested with high range pH tester. pH color chart suggests ~7.4. Double-checked new water sample from tank. pH color chart shows same result.

9:00 p.m. - Set timers to turn powerhead on during daytime, bubbler on at nighttime. Turned system to nighttime status.

Why'd my fish die? My initial reaction is to blame lack of water movement... and then myself for not putting it there. I suppose it could be anything.

I'm puzzled by the rapid change of pH. It seems counterintuitive. If C02 lowers pH, and surface agitation adds C02 as well as Oxygen, then the pH should have been stabilized during the three hours the bubbler was working. It should not have changed in the span of 20 minutes. Could it be that the major areas of my tank were so varied in pH that the increased water movement provided a truer, average sample? I'm missing something.

Help, please.

 

[Philosophos]

Your CO2 gassed off. Air will only push CO2 up around 4-5ppm at most with supersaturation if I recall correctly, where as gassing an angel fish probably takes something like 50+ppm. There's a good difference in pH levels between those two. For a rough approximation, compare to this chart: http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm

If you don't have a drop checker, you may want to pick one up. That chart is very limited in application because of other buffers that happen within an aquarium. Drop checkers are great for getting tanks started and testing problem areas; I use them all the time. I even like to have them in during periods when I can't observe my tanks too often. They won't alert you to every problem, but they've saved me inconvenience often enough to be worth the few dollars that they cost.

CO2 gasses off very fast. Check the graph in this thread; each dot is 24 hours: http://www.barrreport.com/showthread.php/6418-oxyguard-CO2-meter?p=42716#post42716

That tank is incredibly large... 1600-1700 gallons, but it still gassed off within an hour or two.

 

[Tug]

I really don't know what killed your Angelfish. In the year 1917, that would have been a 45 dollar investment down the drain and would have made a grown man cry.

Think of what we see (or don't see) in nature. The Chesapeake bay is devoid of any oxygen. Warmer winters, warmer water and the effect it has on water circulation is killing it. Most of the oxygenated water sits on the surface. In nature just before water freezes it becomes heavier and sinks to the bottom, bringing with it water rich in oxygen. Those days are long gone for the Chesapeake bay. I think we should bring in enormous circulation pumps and burblers all along the bay.

Check how warm you keep the water.
Try lowering it if you can. O2 concentrations in water are higher in cooler water as well.

Filters recreate this circular movement by bringing water to the surface - gassing off CO2 and taking in O2 across the surface. I keep my filter intake (left, back) on the same side of the tank as the outlet spray bar (left side). So, water runs left to right across the surface. Eheim makes a spray bar that comes in sections that can be pointed in different directions. So, half of that outflow is actually aimed tangentially away from the surface. Under that spray bar, a powerhead/neddle wheel is blowing CO2 across the tank. In the right upper back corner there is a Koralia nano pointing down towards the front of the tank. What I am trying to recreate is an undertow. Water goes out along the surface, down and back the other way towards the filter intake underneath. Think of the ways this happens in nature.

 

[justin.sterling.scott]

It's a Non-CO2 Tank...

Your CO2 gassed off. Air will only push CO2 up around 4-5ppm at most with supersaturation if I recall correctly, where as gassing an angel fish probably takes something like 50+ppm. There's a good difference in pH levels between those two. For a rough approximation, compare to this chart: http://www.csd.net/~cgadd/aqua/art_plant_co2chart.htm

If you don't have a drop checker, you may want to pick one up. That chart is very limited in application because of other buffers that happen within an aquarium. Drop checkers are great for getting tanks started and testing problem areas; I use them all the time. I even like to have them in during periods when I can't observe my tanks too often. They won't alert you to every problem, but they've saved me inconvenience often enough to be worth the few dollars that they cost.

CO2 gasses off very fast. Check the graph in this thread; each dot is 24 hours: http://www.barrreport.com/showthread.php/6418-oxyguard-CO2-meter?p=42716#post42716

That tank is incredibly large... 1600-1700 gallons, but it still gassed off within an hour or two.

Maybe we're not on the same page. Or, rather, I'm not on your page. You see, not only do I have a drop checker, but it stays blue. I don't use C02, only Excel. I only dose once every three days right now. I don't think I know what you mean by my C02 gassing off and killing my fish... please explain.

Respectfully,
Justin

 

[justin.sterling.scott]

I really don't know what killed your Angelfish. In the year 1917, that would have been a 45 dollar investment down the drain and would have made a grown man cry.

Think of what we see (or don't see) in nature. The Chesapeake bay is devoid of any oxygen. Warmer winters, warmer water and the effect it has on water circulation is killing it. Most of the oxygenated water sits on the surface. In nature just before water freezes it becomes heavier and sinks to the bottom, bringing with it water rich in oxygen. Those days are long gone for the Chesapeake bay. I think we should bring in enormous circulation pumps and burblers all along the bay.

Check how warm you keep the water.
Try lowering it if you can. O2 concentrations in water are higher in cooler water as well.

I keep the water between 78-80 degrees Fahrenheit. The angels, as well as the plants, tolerate a wide range of temps for tropical water. However, I have read that cooler temperatures inhibit spawning in some fish, mine included; as well as induce fin rot in long-finned species. I have increased the current within the tank... and read a few threads about water circulation and why it is so important (and underrated!) I am going to invest in something gentler with a smaller profile, but for right now it is moving well and the fish are dealing with it. The exercise is good for their little fish parts!

At night, the bubbler comes on. I think this should be adequate. If nothing else, I'll just keep from getting any more attached to the fish and my investment in them.

 

[Tug]

No. You have a nice life!

Sounds as if you have it all figured out Justin.

On a side note Dan was trying to understand the change in pH. Not what was/is killing your fish. To be fair I thought you were adding CO2 as well. I'm note sure why.

 

[Philosophos]

I figured you were running compressed CO2 as well from the description you gave. Turning on an air stone at night is generally a compressed CO2 move as DO isn't a problem with the high level of water movement most planted tanks tend to have.

So, given no compressed CO2, there's no way it was your CO2 levels. Even a 5-10ppm change because of plant metabolism is not capable of altering your pH nearly that much.

Check your KH, compare to past levels. If the KH is off then look for things that increase KH. I'm guessing it's not ammonia; that fish would've had a larger impact than anything else, and that would've been removed just after 5pm, which is plenty of time for it to circulate before your first test. Phosphates would have to go right up through the roof to have that impact.

Did you medicate the tank? Some medications throw off test kits; I forget whether these medications alter pH or just interfere with titration kits. It shouldn't be hard to find out which.

Now as for what killed the angel in the first place, I highly doubt CO2 would be the cause. I suspect a lack of oxygen wouldn't be doing it either, and if it were you'd have seen other fish near the surface.

 

[shoggoth43]

When looking for a fish kill cause, consider the more mundane as well. Is the tank covered? Anyone cook anything recently that put smells into the air? Air fresheners? Bathroom cleaned recently? etc. etc.

Also, excel pretty much dissipates in the tank within 24 hours. So if you aren't dosing every day you may not be getting the full effects that you might if you dosed daily.

-
S

 

[justin.sterling.scott]

I just read that Excel has a half-life of about 11 hours. I reckon I'll start dosing that every day. I had medicated the tank, but that was three weeks and three WCs ago.

Thanks for all the replies! I think, perhaps, that sometimes fish just die. I mean, truly, I bought them at a LFS and who knows what condition they arrive in. I just found a local breeder, so I'll go that route in the future. The pH thing was wierd... if it happens again, I'll let you all know. I added a good amount of water movement and I think things should homogenize well.

As far as the overall wellness of the aquarium, however; I just changed thing radically, as described in a new thread I started. The fish are out of it, and I may be working on it for weeks to come just to get it back in shape.