pH has dropped to 6.0 in a day

[Jack CO]

I have been dealing with the pH in my 10 gallon fry/shrimp tank dropping over time for a while, but it seems to be getting worse. 
I had been using the tank as a quarantine system for 5 petricola catfish as I grew them out and made sure they were healthy. After having them for a couple of weeks I noticed that my pH in the tank was at 6.4, which was extremely strange to me because my tap water is 7.2 and stays there, which I know because my two main tanks (29 and 60 gallons) stay at a pH of 7.2. Having these catfish in with my fry I figured that it was overstocked, which appeared to be the case because my nitrates at the time were about 30 ppm. I have since introduced the petricola into the 60 gallon and thoroughly gravel vacuumed and water changed, as well as adding more plants yesterday. After doing that the pH had been brought up to around 6.8-7 area. I just tested the water again today and am in utter shock to find the pH has dropped to 6 (or possibly lower as the test kit can’t show lower) in just 24 hours. There is no drift wood in my tank, just gravel, a rock, a variety of plants, 5 Ricefish fry, 9 adolescent yellow neos, and my sponge filter. 
I truly have no idea how this could be happening and will gladly accept any advice you can give me. I will attach pictures of the tests from today and the tank below. 

[nabokovfan87]

Hey there,

There is a blog article by the coop that I'll link below. PH is related to your KH value. As the KH drops, then the PH drops. Depending on what your KH is, that would explain the PH issue.

https://www.aquariumcoop.com/blogs/aquarium/ph-gh-kh

If you have one, I would recommend checking your KH with a liquid test kit.

Your test for ammonia might be showing ba sligh hint of ammonia. Given that, I would suggest doing a water change.  Potentially daily water changes.   This will also keep the KH going until you can fix it long term with a buffer or crushed coral.  In my tank I use a product called alkalinity buffer from seachem.

[Jack CO]

I do not have a kh test kit unfortunately. I’ve been doing close to daily water changes of about 40%, so I guess I’ll do another tonight. 
In regards to KH I’ll probably swing by petco tomorrow and have them test for it, and possibly pick up a test kit. 
Is it possible the KH could be different for individual tanks? I’m just wondering this because my two main tanks both have driftwood in them and don’t experience pH drops, yet this tank does without the driftwood. 

[Galabar]

Grab one of these when you go to the PetCo/PetSmart: https://www.petsmart.com/fish/food-and-care/water-quality-testers/api-gh-and-kh-freshwater-aquarium-test-kit-64077.html

Test your tap and the tanks.

Note that you are probably Ok with the values that you however.  However, if you find that your KH is very low, you could consider raising it a bit.  If you are doing regular water changes and your fish seem fine, you are probably Ok.

Edited October 1, 2023 by Galabar

[nabokovfan87]

On 9/30/2023 at 6:48 PM, Jack CO said:

I do not have a kh test kit unfortunately. I’ve been doing close to daily water changes of about 40%, so I guess I’ll do another tonight. 

There is a GH/KH test kit as well as individual ones.  It's anywhere from $7-$11 dollars.  Co-Op sells them as well.

Hopefully you're able to find one and let us know!

On 9/30/2023 at 6:48 PM, Jack CO said:

Is it possible the KH could be different for individual tanks? I’m just wondering this because my two main tanks both have driftwood in them and don’t experience pH drops, yet this tank does without the driftwood. 

It's very possible yes.  You have different loads (catfish might have a lot heavier bioload than others, need more oxygen in the water as well).

Essentially, each tank is it's own situation.  If you're doing pretty consistent, good size water changes I would expect them to be pretty similar, but I wouldn't be shocked if there was some slight variations.

[Jack CO]

Thank you for the help everybody! Hopefully I’ll get to the bottom of this tomorrow