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Unexplained pH drop after water change?


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55 gallon planted community tank: head and tail tetras, pristella tetras, bronze corys, amano shrimp, some nerite and mystery snails.

Fluval 407

Fluval 3.0 set to 50% 7 hrs a day 

The tank has been fishless cycled for about 5 weeks with a mixture of Swords, Crypts, and Ferns. Added pothos plant on top a couple of days ago.

Does with 6 pumps of Easy Green weekly.

PH levels steadied out at 7.5 this entire time. After adding the fish my nitrates rose to 40ppm with ammonia and nitrites at 0.25, so I did a 30% water change with Stability and Prime.

My tap water pH is 8.8+ and is moderately hard, so when I first cycled the tank I added some buffer to lower it to 7.5.

The problem however is that I haven't been adding any buffer when I've been topping off or during water changes, and in the past the the pH stayed steady.

After doing my 30% WC, the pH dropped to 7.2 yesterday and this morning is 7.0

Anyone have any clue what's causing this drop? 

I'm going to do another WC tomorrow because my nitrate level is still a bit high for my liking but I really don't want to keep stressing out my fish.






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So there's a few things we need to do in order to narrow down what is the ultimate cause here.

Especially because of how rapidly you're seeing the drops I am thinking it's more of a water parameter issue than an issue of the hardscape, but let's investigate!

1.  Take a sample of water from your tap, report back test results for KH, GH, PH.
2.  Take that same sample of water, put in an airstone and aerate the water for 24 hours. Then re-test and report those results.
3.  On your tank itself, what is the KH, GH, and PH?


On 6/11/2022 at 9:13 AM, Fishtanker22 said:

, amano shrimp, some nerite and mystery snails.

You also have things in the water besides plants that are going to use up some of the available calcium and could lead to changes if your KH is particularly low or on the edge of being too low.

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Current Tank Parameters

PH: 7.2

KH: 3/53.7ppm

GH: 12/214.8 (I did add Equilibrium for the invertebrates)

Current Tap Parameters:

PH: 8.8+

KH: 2

GH: 8

Will update tomorrow with the air stone sample

On 6/11/2022 at 11:58 PM, Cinnebuns said:

PH drop can sometimes indicate something is dead. That's how I once figured out one of my snails had died. Maybe check on that. 

All snails and fish accounted for. The last nerite was well hidden lol. No deaths other than probably the fry Amano that didn't make it over the past week.

Edited by Fishtanker22
Incorrect measurements and additional info
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