Question on pH reading

[lman]

Quick question on measuring pH and see if anyone has seen this before. I have a tank that has a typical low pH. 7.8 as a low at night and then 8.0-8.1 as a high after the halides have run a while. I decided to measure the pH in a cup (after aerating for one hour outside) to see if I got a difference. pH climbed to 8.1 from 7.9, I then repeated inside and I got the same result. I then measured the pH in a cup with no aeration and it climbed to 8.1 from 7.8 in about 5 minutes.

 

Any ideas on what is causing the problem. I checked the pH in the tank with a salifert pH test and it comes close to the controller pH.

 

Thanks

[zygote2k]

I have the same problem. I'd like to know more about this too...

[Origami]

CO2 build-up. The cup probably has a favorable surface to volume ratio that allows it to blow off excess CO2 while your tank does not. Do you have any way to supply your skimmer with fresh air? What level of surface agitation do you have?

[Rascal]

CO2 build-up. The cup probably has a favorable surface to volume ratio that allows it to blow off excess CO2 while your tank does not. Do you have any way to supply your skimmer with fresh air? What level of surface agitation do you have?

 

Interesting. Could it also be because the cup doesn't have any living organisms adding CO2 to the water?

[lman]

When measuring the pH in the cup, it is within a few seconds of the water being out of the tank. I move the pH controller from the tank to the cup and take the reading. Doesn't seem like enough time for the CO2 to be removed that quickly. I only discovered this as I tried different aeration techniques inside and outside the house to determine if I had excess CO2 in the house. It seems I get a different reading by just having the water in the cup.

 

I don't have any major surface agitation other then the overflows to the sump. I am going to take on of my overflows and raise it in my sump so that it will agitate the water in the sump. I also will try a powerhead in the tank to agitate the water to see if I get an improvement.

 

Before I drill a hole in the wall to pump in freash air I want to make sure that fresh air will fix my problem. Haven't approached my wife about drilling a hole in the side of the house.

 

Thanks

[Origami]

Interesting. Could it also be because the cup doesn't have any living organisms adding CO2 to the water?

 

My guess would be that this is less important in the short time span that we're talking about.

 

When measuring the pH in the cup, it is within a few seconds of the water being out of the tank. I move the pH controller from the tank to the cup and take the reading. Doesn't seem like enough time for the CO2 to be removed that quickly. I only discovered this as I tried different aeration techniques inside and outside the house to determine if I had excess CO2 in the house. It seems I get a different reading by just having the water in the cup.

 

I don't have any major surface agitation other then the overflows to the sump. I am going to take on of my overflows and raise it in my sump so that it will agitate the water in the sump. I also will try a powerhead in the tank to agitate the water to see if I get an improvement.

 

Before I drill a hole in the wall to pump in freash air I want to make sure that fresh air will fix my problem. Haven't approached my wife about drilling a hole in the side of the house.

 

Thanks

 

With today's homes being as well sealed as they are, CO2 levels indoors are often elevated over outside air. If you don't already have good surface agitation in your system, then you should try that first. A film can develop on the water's surface and interfere with air exchange. Having a powerhead agitating the surface can help keep the surface open and improve gas exchange at the surface. Fresh air, though, has helped many aquarists get their pH back up. I don't seem to have much of a problem in my system, but it's kept downstairs and not in our heavily used living areas. If I were to resort to taking fresh air, one idea that I had recently was just to pull it from the attic through the (unused) tube that my builder installed for sub-slab ventillation.