The correct usage of an Auto top up unit (ATU).

Discussion in 'Idol Marine' started by Idol Marine, 30 Dec 2014.

  1. Idol Marine

    Idol Marine

    17 Apr 2012
    Likes Received:
    Auto top units or ATU’s are an essential piece of equipment for your tank. They provide stability and peace of mind.
    Knowing that your water is always at the correct salinity level will greatly add to the stability of your reef aquarium and results in less maintenance.

    How does it work?

    As water evaporates, a float switch in the sump picks up the decrease in water level, this switch activates the pump in the R.O water reservoir that tops up the evaporated water, once the water level is back to where it should be, the pumps stops. ATU’s can vary in design. The simplest versions consist of a float and a small water pump inside a reservoir that will be activated if the water gets too low in your sump.
    The more complex versions, that have a Kalk stirrer, will have a pressure pump, connected to your Kalk stirrer that is connected to a timer or aquarium computer.

    We STRONGLY ADVISE that you have a MAX ON-TIME timer attached when using a Kalk stirrer, a Kalk dump will increase your pH very quickly, and can kill all your livestock.
    The most important reason for keeping the salinity constant is so that your fish and corals are able to adjust to the aquarium. As this is already a stressful environment for your corals and fish, it is essential that they do not have to cope with fluctuations of salinity.
    The oceans’ salinity is totally stable. A fluctuating salinity indirectly causes disease to the fish due to stress, and the corals never settle and open to their full potential slowly deteriorating and finally ending up with a bacterial disease and finally death.
    Adding RO/DI water via a bolus (i.e. all at once) method will cause huge salinity swings.
    RO/DI water has a pH of approximately 7.0 and adding a large amount of fresh water will definitely influence (reduce) your salinity.

    When you own a marine aquarium you have to use reverse osmosis (RO) water, there is no way around that even if you have good quality borehole water for drinking, it is not nearly suitable for a marine aquarium

    All top up water must be from a suitable RO/DI machine, it is important to note that most commercial units (ones that you could purchase from a local supermarket) are not recommended.
    These units contain the incorrect membranes, and adding to the fact that these units have a re-mineralising membrane that will increase your waters Total Dissolved Solutes (TDS)

    Everyone using RO/DI machine should also have a good TDS meter, and the water should never read above 2 parts per million (ppm), even though a number below 6ppm is still acceptable, one should always strive for zero parts per million.

    Below is a picture and an example of a THREE stage RO/DI machine, with one RO membrane and one DI resin chamber. It has a pressure pump as some areas do not have enough water pressure to force the water through the RO membrane.

    How does a reverse osmosis membrane work?

    Reverse Osmosis is a process in which dissolved inorganic and organic solids are removed from a solution. This is accomplished by household water pressure (2.5 – 4 bar) pushing the tap water through a semi permeable membrane. The “impurities” in the water will be trapped by the membranes.

    Below is a simplified diagram of how a RO membrane works.

    Water enters the RO cylinder (1), it then passes through the canister (2) and reaches the membrane (3), all dissolved microscopic impurities leave via the waste gate (5) and clean water leaves (4).
    It is important to always pre-filter the water through a sediment filter and then carbon filters before it enters your membrane.

    Sediment and carbon filters need to be changed every six months depending on your water quality and the amount of water you process, the better you maintain the pre-filters, the longer the membrane will last. Membranes can be tested with a TOTAL DISSOLVED SOLIDS meter to see when it is time to replace. TDS should be below 10 coming from the membrane

    The final step to get clean water is to pass your water through a De-ionising (DI) resin.

    DI resins provide a method to remove all traces of dissolved solids from the water and by utilizing a deionising resin this takes water purification one stage further and will allow for total removal of nitrate and phosphate from the water as well as other dissolved solids.
    The deionising resin traps charged molecules and only allows uncharged molecules to pass through to produce very high quality water.
    Kalk is a very caustic powder, with a pH of 12, 54 at a temperature of 25’C. This pH will kill all your organisms

    The next step in your ATU is to allow your water to pass through a Kalk stirrer.​

    What is Kalk?​

    Aquarists have been using limewater very successfully for many years, and it is the system that we use in our aquariums. It is comprised of an aqueous solution of calcium and hydroxide ions that can be made by dissolving A-grade calcium hydroxide in RO water. Note that the water must be freshwater. Combining calcium hydroxide with seawater will result in a disarray of precipitated magnesium and calcium carbonates and hydroxides.

    Never add Kalk directly to your tank.

    Connecting your ATU via your Kalk stirrer will not only add Kalk to your tank in small doses, but it will ensure that you do not get Kalk powder in your tank.

    Only a saturated solution can be added!

    RO machine.jpg

    ro membrane.jpg

Recent Posts

Similar Threads - correct usage Auto Forum Date
Correct usage of F/2 Powder General Discussions and Advice 25 Mar 2015
The correct photoperiod/ intensity for the correct phase the tank is in! Lighting 4 Jul 2017
Why do people use the word 'siphon' incorrect? General Discussions and Advice 2 Jun 2017
Choosing the Correct Heater for your Aquarium General Discussions and Advice 12 Jul 2016
How to choose the correct return pump Pumps and Waterflow 24 May 2016
The Importance of correct flow in the marine tank. Idol Marine 16 Jan 2015
Selecting the correct plastic for your water drums Test Kits, Controllers, Reactors and Dosers 22 Oct 2013