Ghost shrimp close up, originally uploaded by

Q: CR wrote,

I have a general aquarium question I hope you can help me with. I recently had what I think is a pH crash that quickly killed off my ghost shrimp and several small catfish. I can’t figure out what lead to this and would like to know how to avoid it from happening again.

A: When pH fluctuates in a short amount of time it can be very stressful to fish and especially so when it goes from basic (above 7.0) to acidic (below 7.0). When the pH falls like this we call it a pH crash. If it falls fast and hard enough it can lead to mass casualties. To avoid pH crashes we need to understand what keeps the pH stable under good conditions. Carbonate hardness (kh) is the measure of bicarbonate and carbonate ions in the water and when sufficient, will buffer the pH, keeping it stable. This is why we often refer to carbonate hardness as buffering capacity.

In simple terms, if your carbonate hardness (kh) is adequate your pH will be stable. To determine your kh a simple test kit can be purchased at any local fish store.

0 – 50 ppm very low
50 – 100 ppm low
100 – 200 ppm moderate
200 – 400 ppm high

If you find that your kh levels are very low you may want to add buffers to the water. Avoid the temptation to change the pH level directly with pH-Up, pH-Down or pH-Neutral. These products will cause your pH to fluctuate quickly and won’t solve the problem of inadequate buffering capacity. These quick fluctuations could lead to additional casualties. Adding natural buffers like baking soda to your water will raise your carbonate hardness and help to stabilize your pH. Though baking soda is readily available and inexpensive, some fish hobbyists prefer to buy a buffering agent from their fish store. They’re quite a bit more expensive than baking soda but do the job. If you prefer to buy buffers from a fish supply store, I recommend Kordon’s Dry AmQuel Plus Buffers. It’s a two-for-one in that it acts as both a water conditioner and a buffering agent.

To understand more about pH and it’s role in our aquarium visit Adjusting Aquarium pH Level from Nippyfish: A Betta Blog.

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Reader Interactions


  1. Octopus says:

    Man, I’m glad I was vanity-googling today because it caused me to run across your fantastic blog! This is the first online explaination of the role of kH I’ve run across that makes any sort of sense. Thanks!

  2. Christie says:

    Thanks Octopus! I appreciate the kind words. I mostly focused on low kh levels but I should mention that the converse is true also. High kh levels will keep your pH very stable and difficult to change. In most cases we don’t want to mess with our pH levels but in the rare cases we do. A high kh level will make it very difficult to alter the pH. Welp, just wanted to add that last little note. Thanks again for leaving a comment.

  3. Anonymous says:

    Glad you add the last part about the high KH level. I was looking for info on that! Thanks a lot!

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