Sudden Ph Drop?

madelyn anne
  • #1
Hey there,

I have a 36 G tank with the following;

1 juvenile Angelfish (approx. 1.5" body, 4-4.5" tip to tip"
11 mixed size White Skirt Tetra (1 close to full size, the others are all about 1")
7 SterbaI Corydoras (all of them are roughly 0.5")
2 German Blue Rams, male/female pair (approximately 1.5" right now)

My water parameters over the last 2 weeks have been almost 100% consistent, reading;

pH: 6.8-7.0
Nitrate: 20 ppm
Nitrite: 0 ppm
Ammonia: 0 ppm

The test I did this morning, read;

pH: 6.8
Nitrate: ~30 ppm
Nitrite: 0 ppm
Ammonia: 0 ppm

Tonight, approximately 3 hours post water change, when I tested the water, I got a reading of;

pH: 6.0-6.4
Nitrate: 10 ppm
Nitrite: 0 ppm
Ammonia: 0 ppm

So, obviously a huge drop in pH. The interesting thing is I use Seachem's Neutral Regulator during my water changes, which is supposed to keep the pH at a neutral 7.0 all the time, and since starting it, I've noticed exactly that - almost constant pH of between 6.8-7.0.

So it's really unusual for me to see such a drastic drop in pH right now.

There are no signs of stress in the fish at this time. Everybody seems normal and hungry, aside from my female GBR who's right side of her face turned totally black. This happened about 2 weeks ago and went away, now it's back, and I'm not sure what's going on. No signs of disease or illness in any other fish.

Could anybody please explain why my pH is dropping so much?
I HAVE tested my tap water, and it's actually quite high at the moment. pH straight from the tap is reading about 7.4, so I know that isn't the source. Also, Seachem's Neutral Regulator is NOT a pH lowering/raising agent. It will bring the pH up, if below 7.0, and lower it if it's above 7.0, so that wouldn't be the source either.

Any ideas, anybody?


  • #2
pH is affected directly by the amount of CO2 you have absorbed in the water. Therefore towards the end of the day, there will be a higher pH as your plants use up the CO2 in your water to photosynthesise - producing plant food/energy and O2 which dissolves in the water or floats to the top of the tank as bubbles.

During the night when there is no light, your plants use O2 in the water and burn the energy they have stored up during the day producing CO2 - so in the morning your pH level is naturally higher and in the evening lower. That is what you are seeing with your

pH: 6.8 in morning
pH: 6.0-6.4 in evening

The 0,4-0.6 difference on the pH between the morning and evening readings are ok. However if you want to narrow that swing, then you need to study up on GH and KH parameters - which you can do in this good article here on fishlore.

So to measure pH, you need to measure it at a specific time of day if you want to compare values to a previous reading.

  • #3
u should u lime stone in your tank and texas holly rock
  • #4
You should get a Gh/kH testing kit. It will diagnose definitively a low kH issue versus a CO2 issue.

If you have a low kH, then your pH can crash. kH is the measurement of minerals or buffers in your water. Buffers help keep your water neutral or alkaline. (pH of 7.0+) If you don’t have enough minerals, it gets used up very quickly. Once your buffers are gone, your pH will drop making the water acidic. (pH below 7.0) it has a cascading affect once the buffers are used up. So the pH will continue to drop, and rapidly.

You can increase your kH a couple of ways. All of them do the same thing. You need to raise your calcium carbonate in your water. (This isn’t the same thing as calcium)

You can either add it to your tank in a powdered form, which is baking soda or Seachem Alkaline Buffer. Or you can add it as a solid in the form of rocks/seashells. Aragonite, limestone, Texas holey rock, crushed coral, seashells, or cuttlebone will all work to slowly raise your kH. If using the solid form, you will only need to add it to the tank as it gets used up. It will slowly release the buffers into the tank as needed. Needing to be replaced every few weeks. If you use a powder, you may need to add it more than once a week and with water changes.

So you just have to decide how you want to manage it.

Hope this helps.
Jocelyn Adelman
  • #5
Agree on the kH.... sounds almost textbook. Alkaline buffer is a great product, will raise the kH, bringing the ph back up... just be sure to add it slowly, or the quick climb can affect the fish... best done monitored with the kH test from api....

Is there a reason you use the neutral regulator?

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