5 Tips for Maintaining Stable Salinity in a Saltwater Tank

Comments (18)
  1. Thank you for your post. This is excellent information. It is amazing and wonderful to visit your site.

  2. Avatar Natalie says:

    I have a 30 litre salt water tank, I’m waiting for it to cycle so I can put live stock in, but it needs topping up with water, how can I add tap water without ruining the cycle that I’m trying to achieve, at the moment I’m waiting for the ammonia to drop its on the light green shade?

    1. Avatar Jeff Kurtz says:

      Hi Natalie! Topping up your tank with fresh water to compensate for evaporation won’t disrupt the cycling process at all. Just be sure the fresh water you use has either been purified through RO/DI or at least treated with a product to neutralize chlorine/chloramine.

  3. Avatar yelly says:

    Hello. i need help the salinity of my tank drops to nearly 1.020. What to do? to make my tank again normal?

    1. Avatar Jeff Kurtz says:

      Can you give us a little more information on how you’re mixing saltwater for water changes and compensating for evaporation?

  4. Avatar Jeff Kurtz says:

    Hi Patricia! You’ll want to gradually bring your specific gravity down closer to a natural level (around 1.025). The link below will take you to a post with suggestions on how to achieve this.


    As far as the other readings are concerned, 0 ammonia is good, and your nitrate is okay depending on what you’re keeping. The phosphate level, however, would be extremely high if accurate. Perhaps the decimal is misplaced? Ideally, you don’t want to exceed .03ppm.

    To get a sense of where your phosphate–and all your other critical parameters–should be, check out this article by Randy Holmes-Farley. I think you’ll find it extremely helpful!


  5. Avatar Patricia says:

    My Salinity level is reading 40 & Specific Gravity is 1.030 on Instant Ocean Hydrometer. What do I need to do?
    Also, not sure where these levels are suppose to be and what do I need to do to correct these readings?
    Amonia level 0
    Phosphate 10.0
    Nitrate 10

  6. Avatar Katrice says:


    I found out my salinity dropped below 1.025 was told they have to figure out how to bring it back up. This may sound crazy but for some odd reason the strips I used was not for salinity testing. A little ticked off but I recently purchased a wrasse the day before I found out about the salinity dropped below. What can I do to bring levels up. I am currently waiting on the meter for reading salinity.

    1. Avatar Jeff Kurtz says:

      Hi Katrice! You’ll definitely need to use a hydrometer or refractometer to test your salinity/specific gravity. Once you have it and can verify exactly where your reading is, you can adjust it up or down if necessary. If you need to raise the level, you’ll want to do so very gradually. I usually dissolve a small quantity of sea salt in a beaker filled with aquarium water and drip it slowly into my sump. If the level is significantly lower than it should be, I’ll do this several times over the course of a few days until the desired level is reached.

      1. Avatar Katrice says:

        Jeff…thanks so much for your quick response. If you don’t mind I have a few other questions. I asked the LFS if I needed to do another water change and was advised no. Long story short, I was told that they needed to figure out how to bring up the salinity. They sent out a guy to take out 15 gallons and replace with salt and fresh water but that was something I could have done myself. Just did a water chane on Saturday. It made absolutely no sense. So I am charged for a maintenance fee which could have been avoided. So hopefully the wardley wrasse gets better because it was extremely stressed. Is there anything you suggest I can do to keep the wrasse from dieing? Since they guy came in today to up the salinity I’m still afraid of loosing the wrasse I just purchased. Can I send you a video of what the wrasse is doing? Just to get your opinion?

  7. Avatar Wayne says:

    Hi Jeff,

    Cycle is almost done but I’ve lost about a gallon of water through evaporation. Should I just add the spare saltwater (and do a salinity test) while there’s no livestock to top it up, or get the freshwater instead? The tank is 55g so it’s not a huge amount to top-up and I don’t change it’ll increase the salinity too much. Thoughts?

    1. Avatar Jeff Kurtz says:

      Hi Wayne! You’ll definitely want to use fresh water to compensate for evaporation. Otherwise, your specific gravity will keep rising. Remember, the salt and other stuff dissolved in the water doesn’t evaporate.

  8. Avatar chip says:

    How to do regarding salt creep?

    Above article said ” Over time, this loss of salt can lower the salinity, so you may occasionally need to compensate by adding small quantities of sea salt (dissolved in aquarium water and added very gradually) to your system.”

    can I just drop a scoop of sea salt directly into the tank? small spoon, then measure it..
    wait one day., then each other day do the same
    and keep adding until the measurement hits 1.024?

    originally salinity was 1.024
    right now it is measuring 1.021


    1. Avatar Jeff Kurtz says:

      Hi Chip! I wouldn’t drop the salt directly in the tank. I would recommend that you fill a cup or other small container with aquarium water, dissolve the sea salt in it, and then drip it slowly into a high-flow area of the tank. Beyond that, you’re right on target with the idea of doing this over the course of several days until you get back to your desired salinity.

  9. This is good to know! I’m planning on starting an aquarium in the next few weeks, so I’m doing all the research I can. Water treatment sounds a bit overwhelming at first, but this gave me some direction on how to maintain it. Thank you!

    1. Avatar Jeff Kurtz says:

      It’s our pleasure, Stephanie! Good luck with your new tank, and don’t let it overwhelm you. Take it one step at a time, and keep in mind that only bad things happen quickly in marine aquariums.

      1. Avatar andrew says:

        This article says when doing a water change make sure the salinity is the same as the dirty water…… my question is what if the salinity in the tank is a little high or low?

        1. Avatar Jeff Kurtz says:

          Hi Andrew! If the salinity in your tank is high or low, you can adjust it in a variety of ways. For example, if you need to raise it, you can dissolve a small amount of salt in aquarium water (e.g., in a cup or beaker) and drip the mixture slowly into your sump or a high-flow area of the tank. If you need to raise the specific gravity substantially, you’d want to do this in several doses over the course of a few days.

          Another option for raising the level is to replace dirty water removed during water changes with clean salt water mixed to a slightly higher-than-normal specific gravity or to top off water lost to evaporation with saltwater rather than fresh until the desired specific gravity is reached.

          If the specific gravity of your tank is too high, you can either remove small amounts of salt water and replace them with fresh water or use water mixed to a slightly lower-than-normal specific gravity for water changes.

          Of course, whatever the circumstance or approach you take to remedy it, it’s critical to change the specific gravity very gradually to avoid shocking your livestock.

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