Very high pH Tap Water Unsafe for Aquarium Fish


Fish like Otocinclus catfish are very sensitive to pH changes.

Q: T wrote,

I don’t think my tap water is safe for fish. I tested the pH out of the tap and it was 8.9 and my KH was almost non-existent. What can I do so that it won’t shock my fish? Should I treat with pH Down?

A: A lot of water treatment facilities take measures to alter the pH of your drinking water to make it safer for you to drink. Acidic water can leach lead directly out of the pipes causing lead quantities to reach unsafe levels. To combat this problem water treatment facilities raise the pH to very high levels, usually between 8.5 – 9.3 to keep lead leaching to a minimum. As you may know, carbonate hardness (kh) or buffering capacity determines how stable your pH levels are. If the number is low your pH alters easily and often “crashes”. (Falls dramatically very quickly)

Water that is basic (pH over 7.0) with a very low buffering capacity often falls closer to neutral (7.0) if you age it overnight. I recommend filling a small bucket of water and leaving it to be tested tomorrow. You may very well find that it safe to use the next day. This will just mean a little planning ahead before doing your water changes.

Tank water with very low buffering capacity may experience crashes especially early on when a set up is new. To safely raise your kh you can add baking soda or buy aquarium conditioners like Dry-Buffered AmQuel to use at water changes.

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Christie F is a Betta splendens hobbyist that enjoys spending time caring for her fish and helping new betta keepers learn the ropes. More posts by:

1 Comment for this entry

  1. Dusko Bojic says:

    I like your blog and site. Keep up good work! And enforce responsible fish-keeping!
    http://www.aquariumpoetry.blogspot.com

    Kind regards, Dusko.

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