Simple, Affordable guide to Dosing your reef tank

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    As promised, here is a simple, affordable guide to starting dosing

    Do I need to dose?

    I would love to say no you can get away without, in reality though, reef systems use up magnesium, calcium and alkalinity at alarming rates. Even those of you that have gone down the soft coral route or only a few corals need to realise there are many other processes in your tank that will use these up. Did you think that coralline algae built its hard skeleton from nothingness? What about your snail shells? Microfauna, Microflora, the calcium build-up on equipment, all corals soft or hard still use these up.

    Cant I just maintain these withy regular water changes?

    Not really and heres why.

    Lets suppose, for example, your fresh salt water is 1300ppm magnesium. In a week lets suppose your tank uses up 100ppm magnesium. You do a 10% water change weekly, this will top up some of the 100ppm magnesium you lost but now you start that week with less than the 1300ppm magnesium you want, another 100ppm is used up that week, you do a water change and boost it a bit. However over time you will never replace the amount used up and this element will decline from your reef.

    Why do I need to maintain these parameters?

    The ocean is a vast place, within the ocean the amounts of these big 3 varies slightly geographically. However a reef is only a miniscule proportion of the sea, these parameter spread over the reef will be rock solid, they will not shift. Organisms from the reef need no mechanisms to cope with a shift in these parameters. They have constant unchanging access to all they need to thrive and grow. Presented with fluctuating parameters in an aquarium at best these organisms will not thrive, at worst they will loose colour, become deformed, strip flesh, expel zooxanthellae and ultimately die.

    What should these parameters be?

    This is personal choice, There is a relationship between the 3. I am not going to go into this here, aside to simply mention if your magnesium gets too low, you will never be able to get calcium and alkalinity to hold stable.

    A rough starting point, and what I run my tank at would be

    Alk 8.5 (Anywhere from 7.5-11 is okay but you should try and keep in balance with calcium. i.e if you opt for the lower end of this scale then you want you calcium at the lower end too)

    Magnesium 1300 (Anywhere from 1200 to 1500 is okay, I would consider 1200 a bit low though personally)

    Calcium 440 (Anywhere from 380 to 480 is fine but as above you need to balance it to alkalinity)

    Okay so how do I keep these parameters stable if they are constantly been used up?

    Well you have 2 options, you can add them daily to your tank yourself or automate the process. Many people start to add them manually but soon realise it’s an absolute pain doing it daily and they still have swings as they can only replace what has been lost once a day. If this process is automated these parameters can be dripped into the tank as they are used up.

    How does automation work?


    You have 3 containers of a strong solution of a compound that will raise magnesium, calcium and alkalinity respectively.

    A piece of tube runs from each of these containers to one of the small build in peristaltic pumps on a doser. A doser is simply a glorified programmable timer with a number of peristaltic pumps built into it. From the other side of each pump a piece of tube is then run into the tank or sump.

    At set times each day the doser pumps a set volume of the solution from each container into the tank.

    Sounds easy, but im scared!! You said automated that means expensive?

    It needn’t be! As with all aspects of this hobby you can fit your needs to your budget.

    A 4 pump Doser range from a budget one that will set you back about £30 second hand or £60 new (This is what I use) Premium dosers can run into the hundreds of pounds, having all kinds of bells and whistles, ultimately they are all the same design though. So pick one to suit you.

    Okay I’ve got my doser now what?

    Now you need your 3 containers to hold the stock solutions you will make to raise alkalinity, calcium, magnesium.

    You can buy these containers (expect to pay about £25 per container) or you can make them using a sealed tupaware container, a length of glass or rigid plastic pipe and a wiring lug. (As per diagram)


    Simply cut a length of pipe slightly longer than the depth of your tupaware container, drill a hole in the lid of the container and screw the wiring lug through it. Now insert the rigid pipe through it so the end of the pipe stands about 5mm from the bottom of the container. Finally attach your dosing tubing to the top of the pipe.


    How do I set it up?

    You are probably best keeping the doser and containers under your tank.

    From each dosing container run a piece of tube to one side of a peristaltic pump, from the other side of the same pump run some more tube either into your sump or straight into your tank if unsumped.

    The pipe needs to hang above the water level of your tank/sump to stop back siphoning. You can either DIY a bracket to hold them in place or buy a dosing bracket (£20 upward). I simply tuck mine under the net cover on my tank – I have been meaning to mount the correctly for years, but never get round to it.

    Okay so now we are good to! I just need to go out and buy some compounds to raise alk, magnesium and calcium?

    Well, you can go out and buy the compounds, specifically sold for the aquarium trade. They aren’t cheap and in this guide I won’t go into them as I’ve never used them and having a biochemistry background I am aware that the compounds needed are readily available to buy at a fraction of a cost. This is how to make your 3 stock solutuions (One for magnesium, one for calcium and one for dkh/Alk)

    For the below calculations I will assume we are working on an imaginary 250litre tank, I will show working so you can simply substitute your tank volume in.

    Rather than me show more complex working we will use the following calculator for ease of use for people, to determine how much of each compound effects the parameters in a given tank volume.

    Calculator here:

    The alkalinity stock solution and how much to dose daily
    Lets assume our 250litre tank uses 0.5dkh alkalinity a day

    Chemical required : Sodium Hydrogen Carbonate (NaHCO3)

    Source of this chemical – This is normal bicarbonate of soda (Bicarb) sold in the baking isle of any supermarket. NOT BAKING POWDER!

    Make a stock solution by dissolving 100g of NaHCO3 in 1 litre of ro/di water

    Now using the calculator we can see to replace our 0.5dkh a day in our 250 litre tank we need to add 3.7g of NaHCO3 a day

    Lets scale our stock solution to work out how much to dose daily

    Stock = 100g NaHCO3 in 1000ml of water

    We need = 3.7g NaHCO3 daily

    Therefore = scale factor from 100g to 3.7g is 100/3.7 = 27

    Apply scale factor to our 1000ml of stock solution = 1000/27 = 37

    So we know 37ml of our stock solution will raise DKH in our 250litre tank by 0.5dkh

    2. The calcium Stock solution and how much to dose daily

    Lets assume our 250 Litre tank uses 5ppm calcium a day

    Chemical required : Calcium Chloride Dihydrate (CaCl2.2H2O) This is calcium chloride with 2 water molecules attached.

    Source of Chemical – Buy online (Buy food grade) and make sure if you are following this guide it is the .2h2Oone (i.e Dihydrate)

    Make a stock solution by dissolving 100g of CaCL2.2H2O in 1 litre of ro/di water

    Now using the calculator we can see to replace our 5ppm a day in our 250 litre tank we need to add 4.5g of CaCl2.2H2O a day

    Lets scale our stock solution to work out how much to dose daily

    Stock = 100g CaCl2.2H2O in 1000ml of water

    We need = 4.5g CaCl2.2H2O daily

    Therefore = scale factor from 100g to 4.5g is 100/4.5 = 22.2

    Apply scale factor to our 1000ml of stock solution = 1000/22.2 = 45

    So we know 45ml of our stock solution will raise calcium in our 250litre tank by 5ppm


    3. The Magnesium stock solution and how much to dose daily

    Lets assume our 250litre tank uses 5ppm magnesium daily.

    Chemicals required : MgCl2.6H2O (Magnesium Chloride Hexahydrate) This is magnesium Chloride with 6 water molecules attached

    MgSO4.7H2O (Magnesium sulphate Heptahydrate) This is magnesium sulphate with 7 water molecules attached, also called Epsome salt.

    Source of Chemicals – Online (Buy food grade) you may be able to get Epsom salts from a chemist. Make sure you get the correct Amount of water molecules attached to each compound.

    Either of these chemicals can be used to raise magnesium so using our calculator to raise our magnesium by 5ppm we need EITHER

    10.4g MgCl2.6H2O (Magnesium Chloride)


    12.3g MgSO4.7H2O (Magnesium Sulphate)

    However as we are already dosing chemicals for alk and calcium, using just one of the above compounds will overtime cause a skew in our tank of either Chloride or Sulphate ions. We don’t want this so we need to use a mix of the above 2 compounds.

    I won’t go into why but if you are using the alkalinity and calcium recipes I gave above you need to dose Magnesium Chloride and Magnesium Sulphate in a ratio of 5:3

    So let’s scale the above weights in a ratio of 5:3

    MgCl2.6H2O = 10.4 x 5/8 = 6.5g

    MgSO4.7H2O = 12.3x 3/8 =4.6g

    Lets scale these mass up now and get to a reasonable amount to add to our litre of water for our stock solution.

    An Acceptable amount of stock solution to dose daily would be 50ml. So if we decide to dose 50ml of solution daily, that 50ml must contain 6.5g MgCl2.6H2O and 4.6g MgSO4.7H2O

    So there are 20 daily doses of 50ml in a 1 litre stock, this is therefore our scale factor.

    Now lets scale our mass of MgCL2.6H2O and MgSO4.7H2O up

    MgCl2.6H2O = 6.5×20 =130g

    MgSO4.7H2O = 4.6x 20 = 92g

    So from the above we make up our magnesium stock solution. Dissolve 130g MgCl2.6H2O and 92g MgSO4.7H2O in 1 litre of Ro/di water

    50ml of this above solution will raise the magnesium in our 250litre tank by 5ppm.

    But Wait, My tank isn’t 250 litres like the above 3 examples

    Simply use the calculator and enter your tank volume in litres into it, select the chemical you are adding and the amount to raise daily. Then substitute the weight given into the above working.

    Right so I have my stock solutions in my containers and my doser connected up, I just select a time to dose for each container and click go yes?

    Not quite 2 more things.

    First you need to calibrate each dosing pump (This will be in the instructions) basically just hold the manual dose button for a specific pump until liquid starts tome come out of the end going into the tank/sump. Now take a container of known volume (ideally a measuring cylinder) – usually 100ml container, but the manual will tell you. Now select calibrate from the menu on the doser. The doser will start pumping liquid and ask you to press the stop button once the set volume has been dosed. Job done that pump is now calibrated. Now do the same for each pump.

    Finally you need to set the time and amount each pump will dose. In our examples above lets say we need 50ml of magnesium solution a day. Rather than selecting dose 50ml all at once split it between say 5 doses in a 24 hour period, this helps swings and stability. When you set the times for the other solutions to be dosed try and stagger it and keep doses from different solutions an hour or so apart, this reduces the risk of any chemical reactions amongst compounds you are dosing.

    That’s it you are done now, go and have a beer, you deserve one!


    Just had a quick read Esox, that is dosing the big three 101 right there, this will be very useful for alot of people just starting out on the dosing route, thanks for taking the time to do a comprehensive write up. :thumbup:


    Great effort but one big mistake, a softie dominant tank with water changes does not require any dosing.


    Spelling mistakes etc in It I’ll. Sort out later.

    Re softy tank not needing dosing. I’ll agree to disagree unless you keep it completely sterile. A year from when you set it up all compounds will be depleted, coraline alone will deplete it, before you even get onto other organisms that use it.

    It is chemically impossible to maintain these parameters from just water changes. You physically cannot add what is used back by using the same salt water mix the tank was set up with.

    Anyhow, post was made to help people who pmed me for a guide, not going to get into an argument about what does and doesn’t need dosing.


    I’m sure you’ll have one sooner or later mate


    Fab write up, a bit over my head at the mo but one to bare in mind…


    I’ve run 3 softie tanks without dosing, each one over 5 years. No point publishing a guide if it is factually incorrect.
    This is taken from Randy Holmes Farley Dosing Guide.

    Soft Corals: This includes zoanthids, xenia, star polyps, leathers, mushrooms, and all non-skeletal growing coral. Some even place anemone in this category, but they are technically not corals. Most people that keep softies only rely solely on water changes for their elements and skip out on dosing. In most cases this is perfectly fine considering the growth rates of most of these corals. Keeping them slower is sometimes a good thing, especially with things like pulsing xenia that can easily overpower a reef in no time at all. Some people recommend dosing strontium or iodide, but the most successful way of dosing a softie tank is simply doing weekly 10% water changes. If you feel your reef is not growing then you will need to buy various tests until you find what parameters are actually out of whack and dose accordingly.


    Brilliant stuff matey this will help so many people. Should be a sticky this one Admin ??

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