Everything, including baking soda, causes my pH to fall and my water to become more acidic.

[zebrazebra]

I don't understand what's happening. I have several calibrated pH meters so I'm confident of my readings. I have a goldfish in a 60 gallon tank. I need to do a water change. Tank water is at a pH of 6.45. When I add just a few cups of water at a pH of 7.5 my pH falls (water becomes more acidic.) Trying to do a water change, with higher pH water, is what dropped my pH from 6.8 to where it is now. I have a very low kH and high GH. I removed water from the aquarium and the removed water responds to the addition of more basic water as I would expect (adding higher pH water/baking soda/gravel increases the pH in the sample of tank water) but in the aquarium absolutely everything I do drops the pH.

I tried adding very small amounts of baking soda, which also dropped the pH. That should be impossible. But that is what is happening. Fortunately I added very little but still. This makes no sense. The only thing I can think of is that something, possibly the filter bacteria, are acting as a biological buffer system. I can't safely do a water change until I get the pH regulated because if a few cups of treated tap water cause the tank water to fall by almost half a point then multiple gallons will probably cause a pH crash. I'm trying to move the fish to another tank but I don't have any water within that pH range to move the fish to and I'm concerned the shock will kill her. 

I've tried adding and removing aeration, which made no difference. I've also added a bunch of moss, which made no difference. Adding gravel that I know to be basic from a separate water test lowered the pH (made the water more acid,) as did adding baking soda and adding higher pH (more basic) treated water.  

Anyone ever run into something like this before? The fact that water samples behave normally when outside the aquarium but then deviate from what the actual aquarium does makes me think this might be something biological but I can't think what. 

Any advice appreciated. 

Thanks

[Pepere]

Doesnt make any sense to me either.

 

have you confirmed results with reagent tests as well?

[Galabar]

How are you measuring pH?

[zebrazebra]

Thank you for the replies. 

I have confirmed using both API test kits (two different kits in case one was faulty) which I think are reagent tests as well as pH test strips. Neither are as accurate as my meters but the range they indicate matches the range shown by the meters. 

I have two digital meters which I calibrate using 7.0, 4.0 and 10.0 samples. The meters show consistent results and the pH behaves exactly as I would expect outside the aquarium. 

I found a few people online who had posted about having low kH and high GH and they reported that, at least in the case of water that contains high levels of sulfate, the addition of bases could cause the sulfate to precipitate out which causes a counter intuitive fall in pH. They also noted that law kH caused highly volatile pH. I have sulfate rich water. Their recommendation was the addition of baking soda to stabilize pH and possibly using an RO system and re-mineralizing water on future water changes. Adding baking soda worked with a sample of aquarium water, the pH rapidly rose to 6.96. But when I tried adding small amounts of the resulting baking soda solution to the aquarium the pH declined by .1. I checked again this evening and it seems to have returned to it's original level. If this was a buffer in chemistry I would slowly add a weak base until the acid was exhausted.  I didn't add anything to the aquarium that should act as a chemical buffer, but that's the only guess I have. Also chemical buffer systems I know of don't normally fall below the original pH level, they just prevent change until they're exhausted. 

It is good that the pH came back up to it's starting point 24 hours later. If no one has an alternate suggestion I may try adding small amounts of baking soda to this system over a long period of time until the kH comes up and periodically try my treated tap water to see the pH starts behaving in a sane way at some point. I don't understand why the pH is going down in the first place as that is the opposite of what baking soda is supposed to do in an acidic liquid, even if it is buffered.

[Andy's Fish Den]

 

I am no chemist, and honestly do not test or mess with my water chemistry much other than to use remineralized RO water for caridina shrimp and using RO water and peat to try to get wild discus, angels and corydoras to breed. But, I would look into what is in the tank that could be causing this issue. First, what is your substrate, and decor in the tank? Some substrates will lower pH. I was going to say that your water has low to no buffer to stabilize pH, but you said that if you take water out of the tank, it reacts as you would expect from the addition of baking soda, so that would lead me to believe that it is something in the tank. I would either remove the substrate entirely to test or set the filter up on another tank and test. then, you could figure out whether it is substrate or the biological bacteria in the filter. 

 

[PlaneFishGuy]

@zebrazebra Have you been testing your tap water after it has been sitting out for 24 hours? My understanding is tap water needs to be rested before testing to get an accurate reading. 60 gallons is a large volume of water - I'm surprised that just a few cups is enough to swing the PH. 

Also is the PH causing any issues (unhappy fish, plants, etc)? If not it may not be a huge concern. You could ease in with small water changes and monitor. The stresses of moving fish and lots of changes may aggregate to more stress than the PH fluctuations. 

My tap water and tanks tend to not maintain KH/GH very well on there own. I've had good luck running crushed coral in my filters to keep things stable. Even running CO2 my PH seems to be in a range that is keeping fish happy.  

Edited September 15 by PlaneFishGuy

[Galabar]

I think it's difficult to detect a 0.1 pH change with a digital media inside a tank (and impossible with liquid and strip tests).  If you are putting the meter in the tank, you will see a drift as water moves over the sensor. If you take a sample out of the tank, you are possibly changing the CO2 content of the water, changing the pH.

So, I would say that the baking soda is probably working.  You just added a very small amount and didn't have the ability to test it accurately.

I have a high quality digital meter as well, and just putting it in the tank will see a drift.  Taking a water sample will also see a drift as the CO2 content of the sample changes.

 

Edited September 15 by Galabar

[Mmiller2001]

Use potassium carbonate and ditch baking soda. Use Rotalabutterfly for the amount needed to achieve the KH you want.
Ignore pH, focus on maintaining the correct GH and KH appropriate for the livestock you have.

 

[Odd Duck]

I’m no chemist despite suffering through far too much inorganic, organic, and biochemistry (about 22 hours all together, you’d think I would remember more of it?) for undergrad and grad school, but there’s got to be something in the water that’s dropping your pH.  Letting your tap water sit for 24 hours like @PlaneFishGuy suggested and retesting is an excellent idea to see what your true starting point is.  I also can’t imagine that the very small amount of baking soda added would cause a significant pH shift either way to that much water.  I think like @Galabar noted, it’s very unlikely your pH meter is that accurate with water swirling around.

The more you can tell us about your substrate, hardscape, and plants, the better advice we can generate.