CO2 / PH and keeping fish alive

[jestep]

I have CO2 automatically controlled in my planted tank. This morning I noticed several discus looking really sick, and gasping for air at the surface. My PH controller was reading 7.0, but I did a manual ph check just to be sure. PH was actually at ~6.4, and it looks like the ph probe is failing. This PH equates to a CO2 concentration of about 60 - 70 ppm which is pretty much toxic.

I need to raise the PH to 7.2 - 7.4 or so. Does anyone know of the max speed I can bring the PH up without killing the fish? I could just do a water change and have it up in a flash, but this would probably guarantee dead fish.

I added an airstone to help the CO2 degass, and the plants should bring CO2 concentrations down throughout the day. I figure this is the safer route even though the CO2 levels are way too high. Any thoughts?

[rich311k]

You could do a big water change, the PH from CO2 is not the problem the CO2 is. You need to get the CO2 out of the water. You could just throw in a bubbler or two to gas the stuff off. The PH chamge from CO2 loss will not effect the fish.

[Sarkazmo]

Yeah it sounds like the PH Probe needs replacing. From what I've read they don't last all that long. Be sure to use calibration fluid to setup the new probe. I guess it could be that you just need to re-calibrate the current one, this might buy you some time to get a new probe.

A couple airstones and shutting off the CO2 for now should off gas the CO2 and help re-oxygenate the water. Get as much surface agitation going as possible without stressing the fish.

Good luck and let us know how it turns out.

Sark

[jestep]

I turned off the CO2 and added a huge airstone this morning. They looked better by about 10AM, but I went ahead and did a 30% water change anyway. They look much better after the water change. Ph is also back in a reasonable range indicating CO2 is at a safer level now. Fish still have light stress bars, but aren't gasping or clamping fins like this morning.

They looked about 5 minutes away from death this morning, dark splotchy colors, dark eyes, gasping, clamped fins, swimming sideways, ugh. They were all totally fine when I went to bed, so I assumed something was completely out of whack this morning.

Definitely going to crank down the CO2 until I get a replacement probe and cal solution.

[rich311k]

Good to hear they are recovering well.

[j0hnh0lmes]

Glad to hear all the fish are doing better.

[kennedpa]

Ok....firstly my CO2 switched off at night with the lights. No need for CO2 without lights as no Photosynth will be taking place. No O2 being produced and add co2 will drive your PH down BIG TIME. I also do not use an air stone at all.

My PH raises over night to 7.4 and when the co2 cuts in when the lights come up goes down to 6.99. My PH variance with co2 on is 6.99 - 7.2. The PH goes from the 7.4 to 6.99 preset value over a 4 hrs, from that point the co2 cuts in when the PH get to 7.2.

I know there are people that leave their Co2 going 24x7 and use air stones but frankly that defeats the purpose of plants doing what they are supposed to. As I said, adding Co2 and zero light to create photosynth is a waste of time proven and tried opinion.

Also, my fish are never gasping at the surface, simply because enough O2 is produced during the day and I do not have Co2 pumping in at night playing havoc with my PH.

I would also consider using a PH buffer and keeping your KH @ 6 - 10

[rich311k]

Raising KH in a dscus tank is not a great idea. If his probe had not failed his CO2 levels would be just fine. The PH change from CO2 means nothing, does not bother fish at all.

[jestep]

My CO2 is on 24/7 but since the plants don't use up CO2 at night, and the CO2 is on a controller, it is mostly off at night by default. The probe failed in a way that caused the CO2 to run continuously, so the CO2 concentration by morning was toxic.

PH change wasn't the problem, I was just using PH as an estimate of the CO2 concentration based on carbonate hardness which is what a CO2 controller is doing. CO2 probe failed reading high, which caused the controller to continuously add CO2 to the tank overnight. By morning, fish were dying due to CO2 toxicity, not lack of oxygen.

Anyway, I don't like using buffers in any direction. Over the long term, I've never seen anything but catastrophe from them, and I've been keeping fish for nearly 20 years,

[kennedpa]

I neva used a buffer until I started using Co2 and no ill effects..touch wood. Our water here is really soft hence the use of buffer to maintain the KH at optimum levels as the Co2 levels table in Kaspar Horst and Horst E Kipper's book on the Optimum Aquarium. KH, PH, CO2 and O2 all work together :-)

Keeping fish for 20 years, thats great I have been for 40 years and still learning :-)

Are your 100% certain it is your probe ? Have you checked your Solenoid ??? cuz that is what switches to co2 on and off.

[jestep]

The meter is reading about a full 1 point above actual ph, so it could be out of calibration or the probe could be reading incorrectly. The probe is fairly old, so I'm assuming that it is the cause.

If the solenoid was out, I would assume that the ph would still be reading properly but the solenoid would be stuck open or closed (open in my case).

No kidding about learning something new every day. Especially if you move somewhere with completely opposite water out of the tap. Talk about a difference...

[kennedpa]

Well people have told me the probes usually lat for 12 months, mine is now 7 months old so time will tell.

Indeed there are many variables including where you live. In another state here in Oz, the water is so soft you cant even lather up soap