Figuring out when ammonium levels are too high…

I had a minor freakout at the polytunnel today when on testing the ammonium levels were at 3mg/l. So why are the fish not even the teenyest bit dead? Here they all are – not one lost by the way since aquiring them… yet even the test kit says YOUR FISH ARE ALL DEAD NOW alongside the dubious looking green marker that matches the colour that has emerged in my test tube. I immediately changed up 200l of water (thats what I had de-chloraminated to hand) and got a reading of 1.5mg/l. That was a slight improvement, but should still be enough to do away with my fish within a few days… That is depending on just how much of this reading pertains to toxic un-ionised ammonium (UIA), and how much is of the approximately 100 times less toxic ionised ammonium…

The reading of the colour chart for the ammonium test I have tells you not how much toxic stuff is in the water, rather it indicates the sum mg/l of both ionised and un-ionised ammonium (TAN) . IT TURNS OUT that you need to perform another calculation (ooohhh aaaahhh) before you know what you are dealing with: You need to know your temperature (24 degrees celcius in our case – that is until we get a new heat exchanger), and your pH (7.4 – a bit high, should ideally be 6.8 – 7 for optimum plant growth). You multiply your TAN by the factor on the table below…

Table 1. Fraction of un-ionized ammonia in aqueous solution at different pH values and temperatures. Calculated from data in Emmerson et al. (1975). To calculate the amount of un-ionized ammonia present, the Total Ammonia Nitrogen (TAN) must be multiplied by the appropriate factor selected from this table using the pH and temperature from your water sample. From

…1.5mg/l TAN * 0.0131…= levels of nasty form ammonium of 0.02 mg/l in our tanks today. Anything above 0.05mg/l means the fish are being damaged. We are still falling well short of that. Even with the scary reading of 3mg/l we are at 0.04mg/l~ un-ionised ammonium – still out of the danger zone… for now.

However equilibriums are sensitive beasts… a rise in temperature or pH could shift the equilibrium, causing more of the ammonium to become de-ionised and dangerous to the fish… So now that we’ve detected ammonium, we need to work on reducing it down to almost zero. For now this involves reducing the amount we feed the fish, to let the biofilter catch-up, and also exploring ways to reduce the pH down to between 6.8 and 7…


2 thoughts on “Figuring out when ammonium levels are too high…

  1. Seneye Support Team says:

    Toxic Ammonia (NH3) is very hard to get an accurate level for using looking up tables or calculations. Why? TAM (NH3/NH4) measurement systems can be very mislead as some de chlorinators / ammonia removers cause false readings. Also all measurement devices and systems have some degree of inaccuracy, therefore If you use a calculation or look up table using three measurement systems there is a good chance the end result will be greatly skewed. It’s always better to measure NH3 directly. Time to get a seneye.

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