Q: WC wrote,

Bettas like slightly acidic water but my tap water is basic with a pH at 7.8. Should I add pH down? How fast should I let the pH fall?

A: This is a great question. PH can be confusing and even when you know the numbers knowing what to do with them can send an aquarists head spinning. I will try and keep it as simple as possible. PH is the Power of Hydrogen and measures how acidic or basic your water is. Readings below 7.0 are acidic, readings above 7.0 are basic and 7.0 on the dot is called neutral. This logarithmic scale is used to measure everything from battery acid to lye.

Most aquarium fish live in water with a pH range between 6.5 and 8.0. Individual species thrive best in water with a pH close to their natural environment. This can prove to be challenging if your fish is adapted to the acidic water of a Malaysian rice paddy but the water pumped into your house is basic. Commonly, an aquarists first response is to panic and dump in drops of pH-Up or pH-Down to “fix” the problem. If this describes you then the first thing I need to say is “STOP, and put down the bottle. Now slowly step away.”

Yeah, ok, I’m being a little dramatic but I have good reason. Here’s why you should think twice before adjusting your waters pH.

First, that logarithmic scale I was talking about earlier… Well that means the units are being measured ten-fold. That denotes a pH of 6.0 is 10x more acidic then a pH of 7.0 and a pH of 5.0 is 100x more acidic then a pH of 7.0. Sure, the numbers seem so small (5, 6, 7) but their impact can be serious. A rapid fluctuation, especially toward acidic can cause what aquarists call a “pH crash”. This is when the pH drops quickly and everything that once was living is now compost in the bottom of your tank. Within a matter of a few minutes, every fish in your aquarium can die from a rapid and sever pH fluctuation. If severe enough it can even kill off all your beneficial nitrifying bacteria.

The second thing to consider is your carbonate hardness, also called buffering capacity (KH). Simply put, water with a high KH level is well buffered making it difficult to change the pH. You’ll have to add a lot more drops of that pH-Down in well buffered water then in water with a low KH level. Very low KH levels can mean the pH may fluctuate on it’s own and in some cases pH crashes occur naturally. Many major cities treat their water so the KH is very low allowing the facilities to alter the pH levels before pumping the water out to the masses. It’s a great idea to test your tap water’s KH so you have an idea of your buffering capacity. If your KH is very low or high you may struggle with keeping your pH stable. As mentioned earlier, unstable pH is much more dangerous then one that isn’t ideal but stable.

The third thing to know is that most fish, including bettas, can adapt to your water’s pH levels. Bettas can do very well and live long healthy lives in a pH of 7.8. The important thing to understand is that in basic water, toxins like ammonia and nitrite become exponentially more dangerous. Since your pH is high you will need to be very diligent about your cleaning regimen and I strongly suggest anyone with basic water cycle a tank for their betta rather then using a betta bowl where 100% of the water is changed regularly.

So before you reach for that pH adjuster bottle, think twice and consider if your betta will be better off without it.

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Reader Interactions


  1. Betta Fan says:

    I am struggling with the death of my betta. I lost him on Friday, after having him for a year and 4 months.
    He was doing just great until 2 months ago when he started hanging around at the bottom of the tank more. I did tons of research and thought the problem was two-fold: water was too cold and I was not leaving some of the water in the tank when I cleaned it. So, I ran to the store and bought a good heater (I have a 5 gal. tank with air filtration and a light) and for the last two cleanings, I vacuumed the gravel and emptied some of the water, but not all of it.
    This was the first time EVER that I didn’t do a 100% water change. Now, I am afraid that by not cleaning the tank properly (I still don’t know how to clean it since you aren’t supposed to change it 100% and yet when I stopped doing that, coincidentally, he died), the PH level plummeted (I had it tested and it was very, very low) and that is why he died.
    I put him in an iso tank for the last few days he lived, but it wasn’t enough to save him. Since a lot of folks say they live for 2 or more years on average, I wondered if age was a factor or not. I am agonizing over this and afraid to get another betta if I did something to kill my beautiful Nemoby.
    Did the gradual lowering of PH kill him? If you are supposed to leave some of the water at the bottom when you clean, how much? How much of the residue should be vacuumed out? How do you know if you have enough of it out so the PH doesn’t drop?
    I appreciate any suggestions toward what killed him and and help in getting through this sad experience.

    • Danyael Dacanay says:

      Yeah age could also be a factor and I think it really is but did you consider the age of the betta when you got it from the store? try adding it and mine lives for 2 years and when it goes over 13 or 14 months I give it away to children to intoduce the hobby heehehe 🙂

  2. ganchome says:

    Can you point to a website that explains what you mean by “cycle a tank”?

  3. farruu the Fish girl says:

    The death could always be from water temperature or disease but it wasn’t your fault for the fishes death.

  4. a says:

    I like full water cleaning; partial does not get “bad bacteria”; as well;;

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