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Maintaining Alkalinity Calculator

Maintaining the alkalinity is very important in any recirculating aquaculture or integrated aquaculture system where there is a biological nitrification process.  Unfortunately it is often overlooked and many simply focus on the pH of their systems.  It is important to understand the alkalinity level is the capacity for your system to buffer against acid production in your system, which in turn maintains a stable pH. Without Alkalinity your system pH can crash.  When the pH falls below 6 the immune systems of your fish are compromised so any stress will generally create a path for infection and often death and your bio-filter capacity to complete the nitrification process may stall due to the low carbon content in your system. In a previous newsletter I put together some basic rule of thumb numbers on the amount of alkaline supplements required per kg of fish feed for a variety of commonly use compounds. I have taken this a step further for you and put together a free calculator for estimating the required amount of these alkaline compounds related to the protein levels in the feed and how much feed you apply each day.  This is a little more exacting in comparison to the previous table, though the calculator is where that table originated from. There are two “special” questions in the calculator that relate to plant integrated aquaculture systems which change the results considerably.  One is “Is it a planted system with an independent biofilter”?” and “Is it a planted system without an independent biofilter?:” There reason for these two extra questions because of the carbon cycle in planted systems makes predicting alkalinity need difficult.  Planted systems are effectively denitrifiers which contribute to alkalinity production. Understanding how plants effect the alkalinity is important in your integrated aquaculture system. Firstly, there will be a combination of nitrogen uptake in any system.  Young plants (up to 2 to 3 weeks) will primarily take up nitrogen in the form of ammonium because they lack the enzyme that converts nitrate to ammonia for root growth.  This process or ionic exchange will produce hydrogen or acid and consume alkalinity. Remember that NH4 and NH3 make up your Total Ammonia Nitrogen and the root ion exchange when ammonia is taken up as a nitrogen source is the hydrogen (H) is basically put back into the water.  The more hydrogen, the lower the pH or more acid is produced.  While this is a very simlified explanation, it covers the basics of the reactions. Secondly, mature plants that have the required enzyme will primarily take up nitrogen in the form of nitrate.  When they do this the exchange creates hydroxyl ions thereby increasing or contributing to the alkalinity in your integrated aquaculture system. In a correctly sized system where all the nitrate is being taken up, you should not have any need for adding alkalinity supplements however this is a very rare case is smaller, more dynamic systems at home. Because you will have some young and some older plants in the system it is difficult for me to predict how your carbonate system will respond to feed input so these questions will help estimate the required addition of alkalinity supplements. I stress this is not exact because I can not know your system, so measure your alkalinity before adding the amount the calculator tells you.  Add it over time, not at once.  In time, as your system settles down, you will come to know how much it needs and if you consistently add the required amount to counter the pH drop, your system will become very stable and productive. In pure recirculating aquaculture systems where water is not being returned from a denitrifying filter (eg hydroponic subsystem), the calculations assume you have good solids removal and no anaerobic pockets in your treatment processes.  These anaerobic areas will denitrify through bacterial process and act similar to plant integrated systems in regards to alkalinity.  Basically they will add alkalinity without producing any growth. Testing your alkalinity and getting it to a level that is optimum for your biofiltration nitrification process and adjusting alkalinity treatments to suit your particular system is best practice.  This calculator will help predict what your system will need.  Always rely on actual water quality tests before adding anything to your system. You can download the free alkalinity maintenance calculator here. Enjoy Paul…

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