[From the Archive] Mr. Saltwater Tank TV Friday Am Quick Tip #61: Nail Your Salinity Every Time

Forget remembering how many cups it takes to reach 1.025. Use this tip instead.

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Comments for this article (19)

  • Kerstin says:

    Instead of a premeasured container like this, I use a container and a scale – I know it always weighs the same amount out, and since I use this scale all the time for weighing out flour, it isn’t any hassle. Although I like this one too.

  • Mohamed says:

    Yes, I do this always.


  • Bryan says:

    The other end matters too. How much salt water do you take out of your tank? I use a siphon and buckets and I have a mark on the side of my tank, but the amount that I take out is not exactly the same every week. And if that is the case, then the amount you put back in will vary too. So I always still check my salinity as I add salt to my holding tank to be sure I get it back to the correct level.

  • Jon says:

    Hmmm….Bryan- indiscepencies in terms of how much water is being removed on a weekly basis should not effect the amount of salt you adding…water in the display should be 1.025/6 and the new water that you are making, and subsequently adding should be the same…enjoy

  • Jeremy says:

    Jon not true. I learned this the hard way by putting in more salt water than I took out during my water changes. I did this routinely for around 2-3 months. At the end I found my salinity up around 1.029 in my display. I figured after the evaporation it would level it self off but I have an ATO and keep my tank at a very specific water level. By exceeding that level continuously the extra salt caused my salinity to increases due to the evaporation level since salt stays in the system.

  • Marcos says:

    I use a premeasured container, but with half the dose. I dissolve them in two steps, allowing the first dose to completely dissolve to then add the second. This way I avoid precipitation of calcium/carbonates and build up of these in the container walls.

  • Merne says:

    Jeremy and Brian, you must be adding all the saltwater you just made rather that just the amount you removed from your tank. I have an ATO dedicated for water changes with a float switch at the same level as the freshwater topoff switch. When I do water change, I plug in this ATO. When I’m done with my water change, the tank level is still the same. True that if you add more saltwater than was in your tank, evaporation will increase the salinity over time until the level reaches your freshwater ATO. I hope you can find a good way of doing this instead of guessing what salinity your chane water should be.

  • Darsh says:

    Good idea. I use the free cups you can get at petshops to measure your dogfood 🙂

  • Jeremy says:

    Merne, You are correct I was doing this in the beginning but have since started matching the export to the import and no longer have this problem. Still looking at a way to automate water changes just haven’t had the time to build it 🙂

  • Eric Fisher says:

    I use the scale below. It allows you to use any container you want and make any amount of saltwater. Set the container on the scale, zero the scale, add salt 1.025=(1.6 lb / 5 US gal). If you want to make 26gal of saltwater you would need. (26gal / 5 *1.6) = 8.32lbs of salt.

  • Easyflip says:

    Just cut the container at the line and add 1 topped off container, super easy. And in a water change why wouldn’t you remove and add back the same amount of water? What possible reason exists to make more trouble for yourself? Just sayin’

  • Kyle O says:

    I agree with both Marcos and Merne. It is important not to add all of the salt that it takes to make 1.025 SW all at once as it will precipitate and you will not be able to put the total amount of fresh calcium and carbonite into your during that water change as you could/should. Mixing up slower and let mix for a day before gives you crystal clear 1.025 SW.

    I am also a big fan of making sure that the salinity is actually 1.025 before it is used in the water change. Too many small variables to use the mix and go method.

    I have also found that always having a large batch of fresh saltwater on hand has saved my butt a few times……like when the skimmer goes crazy or a hose springs a leak on the calcium reactor. Being able to get the sump filled to where it should be immediately is one less thing to stress over in an emergency fix/cleanup situation.

  • Bryan says:

    I may have been a bit confused with my explanation. My saltwater holding tank has 30 gallons of salt water. My display tank has 125 gallons. I take out roughly 15 gallons each water change. So my saltwater holding tank will re-fill with RO water up to the amount I took out of my display tank (say 15 gallons). So I have to add back in the amount of salt needed to get my holding tank back to 1.024. The amount of salt I need to add back to my holding tank is proportional to the amount I take out of my display tank. If one day, I take out 18 gallons from my display tank, then I had better not add the same amount of salt back to my holding tank as I did when I took out 15 gallons of water from my display tank or my salinity will be too low. Likewise, if I add the same salt after taking only 12 gallons out, my holding tank salinity will be too high. So I always check my holding tank salinity after it refills with RO water so I am sure I only add the amount of salt needed to put the salinity of my holding tank back to the correct level.

    Then there is the other problem already mentioned where my ATO will add RO water to a preset level, so I always need to be sure I refill my display tank to the same level every time. And indeed, if, while I am removing water from my display tank, I do not close the valve from my ATO, then RO water will start refilling my display tank before I am ready to add the premixed salt water and that too can cause my display tank salinity to be too low. Then I just recently discovered if my overflow gets clogged a bit with algae or plant material, it slows down the rate water returns to my sump and again, my ATO will kick in and fill my sump with too much RO water. For the most part, everything works well. But I feel the need to keep a close eye on my salinity in both my display tank and holding tank.

    Thanks for all the good ideas!

  • John says:

    I do and easier is what Eric does use a scale.
    Or I have a 50 mix tank and I need to work fast have per made container of salt for that 50 gal mix tank and dump in all done add water.

  • Pierre Bouic says:

    Well its easy to see that many of us are using different ways to essentially get to the same outcome. Not all of us use an ATO, but we all should be heating the mix & aerating the salt mix, I do this with a power-head that breaches the surface while stirring & giving a even heat. Small differences occur in salinity at different temps eg. 1.025 at 68 f has a difference of.0011 of salinity, compared to 78 f = .0027. This sounds negligible, and won’t matter as long as you test the display tank salinity before draining the amount of changed water, then test the mixed aerated water before adding, and finally a test of the tank after one revolution of total system volume to allow for the different area’s to receive the new water, like the mud box, refuge tank filter sump, to turn over.
    If using a plastic specific gravity type of tester, its important to flush tank water thru it several times to get relatively accurate salinity measurement. Those testers can be inaccurate especially if not soaked for 24hrs in fresh water of the temp being used before to condition the weighted needle arm. I use one of these to give a quick salt content but always fill & empty several times before taking a look, and always rinse in R.O water after. Lastly salt water is thinner when warmer & thicker the colder, this is why a refractometer is the only accurate devise to use because of its ability to compensate for water temps variability.

  • MikeG says:

    I use some digital kitchen scales that I purchased solely for salt water making. Each new bucket of salt I buy, I make up a reference 10l of salt water noting how much salt is required to make it. So if it takes 35g per liter of salt to make it up to 1.025 salinity – then this makes it easier for bulk measurements. So for a 100l water change I just need to weigh out 3.5kg of salt.

  • Frank says:

    I used a sharpie to draw a low and high line for my ATO in the sump. When I refill for the water change I’m usually within 1 to 4 cups. 180g DT and 70g sump.

  • Nikolaus says:

    Ok a couple points to make here. 1 all salt is different. you cant just say 1.6 lbs per 5 gal or whatever, some are more dense some are less. and for quantity, i use 5 gal buckets and siphon to one point fill to the same.

  • Marc says:

    No matter how you make (or buy!) your saltwater I believe you should ALWAYS check the salinity prior to adding it to your system. There are too many variables including some that are outside your control, ie you might get a bad batch of salt even from a company you’ve been using for years, it may not have disolved properly, the humidity and temperature may be different, etc. I use many of the same methods listed here such as premarked containers of water and a scale to weigh out the salt – but I still check it before adding the new water to my system.

    I also use a Kalkking for my ATO. Since it is used to stir/dose my kalk it allows me to set the rate at which it adds either kalkwater or straight RO. I keep it set at a very slow drip rate so even if I forget to turn it off during a water change it’s only going to add an minute amount of straight RO or kalkwater before I finish the WC, not enough to change my SG by even .001 (it also has a built in PH controller which makes sure that I never overdose kalk, even if I screw up and don’t refill the system with the correct amount of water.)

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