- Is this fish good for my tap water?


Is this fish good for my tap water?

Author: Yeo-Hoon Bae
Last Updated: Nov 5, 2009

You went to the local fish store. You found couple of fishes you like. You wrote down their common and scientific names. You came back home. You did some homework. You went to some fish profile web sites (if you haven't yet, you know what to do first!) and found out that your the pH requirement for your favorite fish is outside of your tap water.

So what are you going to do?


First thing to realize is that most fishes are surprisingly forgiving when it comes to pH levels. Even though the fish profile sites may say they need acidic water, many people will be able to raise them in water with pH levels as high as 7.6. Yes, even difficult fishes such as Discus can be raised and bred in these pH levels. But pH is not the end of the story. There are several things you should be aware when you are looking at the characteristics of your tap water:

  • pH - Most fishes can handle very wide range of pHs, often much wider than the numbers suggested by fish profile pages. In most cases, you don't need to change it.
  • GH - General Hardness. This is in fact more important than pH. It measures the level of Magnesium and Calcium in water. In most cases, once again, fishes will be able to adapt to wide range of GH levels.
  • KH - Carbonate Hardness. This measures the water buffering ability. Lower level means more likely to experience pH swings. Higher level means more stable pH.

  • One thing to keep in mind is that your tap water is likely to contain more CO2 than your tap water that has been sitting in the bucket over night. Higher concentration of CO2 will cause pH to drop. To measure correct levels of pH, you should collect water from your tap, let it sit over night, then measure it. In most cases, you will see higher pH reading compare to water directly coming from the tap.

    If you have test strips, go and buy a liquid based test kit now! Strip tests are very inaccurate and will often report misleading readings.

    Real life examples

  • Question: My tap water (after letting it sit overnight) says 7.6. GH is 8 and KH is 8. I want to raise German Blue Ram which requires pH between 5 and 7 according to my favorite website. What do I do?
  • Answer: Nothing. When you purchase your Ram, make sure you take time to acclimatise them slowly. i.e. Take a bucket, empty your bag of Rams into it. Then over few hours, slowly add your tank water into the bucket. When you roughly doubled the volume of water, you are ready to catch your Rams and add them to your tank. (Using quarantine tank is highly advised!)

  • Question: My tap water (after overnight) says 6.2. GH is 1 and KH is 2. I like African drift lake ciclids but I have been told they need really hard water with high pH. What do I do?
  • Answer: In this case, you will likely to need to adjust your water chemistry. There are several ways to raise the hardness of your water. Common approach is to get a bag of crushed corals and add them into your filter. Also use them as your substrates. You can add rocks that increases water hardness. Limestones and Texas holey rocks will do this for you. Lastly, you can add baking soda and epson salt. Amount will depend on how soft your water is.

  • Question: My tap water is 8.0, GH is 20 and KH is 25. I want to breed Discus. I think this water is too hard. What do I do?

  • Answer: Your water is really good for African drift lake cichilds! Some people will kill for that water! One of the sensible things you can do in this hobby is to choose species that will thrive in your native water condition. Chaning water chemistry is always tricky and keeping them stable once changed is even trickier. Look into Lake Malawi or Tanganyikan species. If you don't like them then you will have to lower your water hardness. One of the most common approach is to use peat moss. You can get a big bag of sphagnum moss from your Home Depot or Lowes store. These peat will soften your water. If it softens enough, pH will also drop. The other approach is to add RO (Reverse Osmosis) water but this is an expensive solution that only few serious hobbyists should look into.

  • Summary

    It is often best to not mess with your water chemistry. Most species will be able to adapt to your water unless they are extreme at extreme levels. If your KH is too low, you are risking a big pH swing which is not a good thing so in that case, it might be wise to add some crushed corals in your filter. One of the key things to realize is that most species can tolerate some pH swing. If you can keep your general hardness level consistent, you are going to be ok.

    You can further discuss or leave suggestions in this forum.

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