Dont lose fish Check your pH after Rain! Grab your test kit, do it Now.

Dont lose fish Check your pH after Rain! Grab your test kit, do it Now.

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Why You Should Check pH After Rain 

Rainwater is naturally acidic — usually with a pH around 5.5 to 6.5. When it enters your pond, it can lower the overall pH, especially if your pond has low KH (carbonate hardness), which acts as a buffer.

How pH Affects Oxygen in Your Pond

  • pH doesn't directly create or remove oxygen, but it affects how available oxygen is to your koi.

  • When pH drops below 7, especially below 6.5, it becomes harder for fish to absorb oxygen through their gills.

  • This can be dangerous — especially for large koi, which need more oxygen.

Why Nighttime Makes It Worse

  • At night, plants and algae stop photosynthesizing (no sunlight), so they stop producing oxygen.

  • Instead, they consume oxygen — just like your fish do.

  • So now you have:

    • Less oxygen is being made

    • More oxygen is being used

    • And low pH makes it harder to absorb oxygen

This combination is what can suffocate your largest koi overnight, especially if pH drops after rain (acid water).

What You Should Do?

  • Test pH after every heavy rain, especially if your pond isn’t well-buffered.

  • Keep your KH levels up — use crushed coral, baking soda, or commercial KH buffers to maintain stability.

  • Aim for a pH between 7.6 to 7.8, and never let it swing suddenly.

  • Ensure good aeration at night with air stones or waterfalls — this helps maintain oxygen even when plants stop producing it.

     pH, Rain, and Oxygen

    After Rain

    • Rain lowers pond pH — especially dangerous if KH (buffering) is low.

    • Check pH daily after rain — use a reliable test kit.

    • Keep KH levels stable (90–150 ppm) to prevent pH swings.

    ⚠️ Why Low pH Is Dangerous

    • Fish struggle to breathe, even if oxygen is technically present.

    What Happens at Night

    • No sunlight = plants and algae stop producing oxygen.

    • Everything in the pond uses oxygen, including koi and bacteria.

    • Low pH + low oxygen = danger zone for large or sensitive fish.

     

    Tip:

    If your pond has green water or lots of algae, it may produce oxygen during the day but steal it back at night — causing overnight oxygen crashes when paired with low pH.

    pH below 7 reduces oxygen availability to fish, add in warm water, it's a disaster waiting to happen