Marine water chemistry explained

Mastering water chemistry in a reef tank is just as key to success as using the right lighting. Maybe even more so. The chemistry of the earth’s oceans has remained unchanged for millions of years. Take a water sample from the Arctic, Atlantic and Pacific oceans and their chemistry will all be very similar. 

Corals have evolved and adapted to those unchanging conditions, and change is something they’re not good at, as we see in the news what a rise of a few degrees temperature can do to them. They’re specialists, not generalists, just like all the other reef-associated creatures. 

Starting off right

The chemistry of marine salt mixes is made up to be the same as that of the oceans. D-D salt and Red Sea salts are actually made from evaporated seawater, while others are made from high-grade synthetic materials. Mix them with RO water to the right salinity and you will be able to provide high-quality seawater at home. That’s the first step.

But get the salinity too low and all the other parameters within that salt will also be wrong. That’s why it’s important to always measure saltwater with a refractometer – a measuring device purpose-built for the job. Temperature is important too when mixing salt as refractometers are calibrated at 25C. So always heat the water to the right temperature before taking a salt reading.

Maintaining chemistry

But even if you start off with good water, corals will use up elements to build their skeletons, deplete the water, and that’s where most reefkeepers go wrong. In the oceans the levels of KH, Calcium, Magnesium and others never deplete, so again corals have never had to evolve to deal with it.

Add several corals to your aquarium and levels of KH, also known as Alkalinity, can drop on a daily basis. Corals cannot survive in low alkalinity so it should KH should be replenished either by regular water changes or by adding buffers. 

The next two important parameters after KH are Calcium and Magnesium. Most reefkeepers are aware of the need for Calcium to be added to their tanks, but not everyone knows how much, and the importance of buffering other parameters at the same time.

Add Calcium without testing for it and when it gets too high, it will reach a limit and just precipitate out of the water. Have low KH, Magnesium and other parameters and no matter how much Calcium you add, your corals still won’t do well because they will be deficient in other elements. 

Testing and Dosing

So not long after setting up a reef tank, and adding your first corals, you should begin regular testing for salinity, KH, Calcium and Magnesium. They are the big four, and the ones you need to master before taking dosing further. 

Start a daily log and record levels of all four. You will notice that the KH will be first to drop. Purchase some KH buffering solution and add it in small amounts until the KH comes back up to what it should be. Right down how much you added in order to raise KH to the right level, e.g 50ml.

Log over the course of a week how much KH buffer you needed to add to keep it at the set point. If you had to add 50ml of KH buffer three times in a week to keep it constant, your tank’s consumption is 150ml of KH buffer a week. Back to that in a minute.

Do the same with Calcium and Magnesium readings. You’ll then know exactly how much of each your tank consumes in a week. Add them to your tank every week and you’re halfway there to holding water parameters where they should be, just like natural seawater.

The Balling Method

Dosing those three elements regularly is a method known as the Balling Method, developed by Mr Balling at German salt manufacturers Tropic Marin. If you want further stability install a triple auto doser on your system, specifically designed to dose liquid KH, Calcium and Magnesium.

The advantage with an auto doser is that it can not only dose your 150ml of KH to your tank per week. It can also split that dose into tiny amounts throughout day and night, 24 hours a day, seven days a week. This means that the tank water chemistry is constantly replenished as soon as it becomes depleted and the corals never suffer from feast or famine. Again, stability is key.

Balling light

But there are over 50 elements in seawater, and we are dosing just three. This is good, but not as good as including some of the other elements that corals also need for health and growth. Not all of the 50 elements are vital to corals, but several are. Cue Balling Light.

Balling light adds other essential elements to the tank at the same time as KH, Calcium and Magnesium are being dosed. Available either in liquid or powder form, the extra elements are either added by you to your three existing dosing containers or are available pre-mixed by the manufacturer.

The good news is that you don’t really need to test for the other elements and instead just be reassured that as your doser doses Calcium, for example, its also dosing other essential elements that have been mixed with it at the same time.

Many of the world’s reef care programmes are based on Balling Light and are very successful. You just need Balling chemicals, test kits, bottles or containers, and a triple auto doser.

Triton

The Triton Method goes a few steps further still. You start off with good saltwater in the tank, and you dose just like with Balling and Balling Light. But instead of using your own hobby test kits you send the tank water off for ICP-OES analysis – very high-end professional testing – and the test comes back telling you which out of dozens of different elements need topping up, and dosing.

Triton also supplies all those individual elements so if the test says you are low in Strontium or Vanadium, for example, you can add it and get your depleted water back up to good as new water, and back to being perfect for growing corals.

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Jeremy Gay is an author and freelance aquatic specialist. A former editor of Practical Fishkeeping magazine, he offers a wealth of experience on all things aquarium and pond.


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