With test of oxidation he means that if the tank will be spiked with NH3/NH4 (around 2 ppm) and if it is 0 after 24 hours - the tank is cycled in his opinion.
IMO - it is both right and wrong. The nitrification cycle is in reality two processes
1) Many types of bacteria and archaea convert NH3/NH4 (ammonia) into nitrite
2) A few types of bacteria with low growth rate (nitrobacter, nitrospira) oxidize NO2 (nitrite) into NO3 (nitrate) (nitrobacter, nitrospira)
The NH3 form of ammonia (unionized ammonia, ammoniac) is toxic for fish. Because the NH3 part of the ammonia complex is higher in high pH environment - NH3 toxification is more common than in fresh water
NO2 (nitrite) is highly toxic for freshwater organisms - not so toxic (or toxic at all) for saltwater organisms. This is depending of the way NO2 is taken up by gill breathing organisms. It takes up through transport channels in the gills but high chloride contents in the water (above 80 ppm) will block this uptake. Saltwater contain around 19 900 ppm!
In this part - @brandon429 is right - if the system can process a certain amount of ammonia during a certain time - the inorganic N compounds will not cause any toxicity for saltwater organisms - but in my eyes - it is only a prove that the first step in the nitrification process is up and running.
It has been show that it sometimes can be a "hung" between step 1 and step 2 and nitrite will be build up - in freshwater very deadly but in saltwater of no concern according to toxicity. But a NO2 build up means that the total nitrification process is not completed and for me - it is important that it is completed and monitoring the NO2 level is a safe way of knowing that both step 1 and 2 works seamless.
Most "ammonia" test monitoring both the untoxic form (NH4) and the toxic form (NH3). You must know the pH and temperature in order to know if your total ammonia content is toxic or not. IME - these type of hobby test nearly always report a total ammonia content of around 0.25 ppm and cause panic among aquarists. There is one test (I have not tested it) that claim only to show the toxic form (Sea Chems ammonia alert) . What I have read - it is a good test often used in QT tanks. Summary - total ammonia tests is often not easy to use and often give a false reading.
Is it not better to test in the other end - if Nitrate is produced - the whole cycle is completed?
It seems to be a good way - but - it is always a but - all hobby tests I know of works in the same way. A metal complex is used to convert nitrate into nitrite. In the second stage - nitrite is analysed. The colour scale will transfer back the result as nitrate.
This process is slow (can take many hours) and therefore most test is constructed that after a certain time x % is converted - the colour scale is compensated for this and convert it to the expected nitrate concentration. This means that - if it is nitrite in the water from the beginning (a hung in the nitrification cycle) you get a false NO3 reading. The conversion factor is normally 50 but some brands can have a factor of 100.
This put together - both testing in the beginning of the cycle and after the cycle can be problematic .
On the other hand - nitrite testing procedures is often very good even with hobby tests - at least in concentrations above 0.01 ppm. (will alter the nitrate reading with around 0.5 ppm).
The first step will start in a couple of days (if you have an ammonia source in the water) and after a week you can start testing the nitrite level. The best test that your nitrification cycle is total completed is if you test below 0.02 in nitrite and over 3-4 ppm nitrate.
Summary:
Brandon is right if you with cycling mean no toxic forms (in saltwater) of inorganic N species but he can be wrong if you see to the whole nitrification process. The oxidation test a la Brandon show that the toxicity of N species is under control but not - IMO - that the total nitrification cycle is completed - To know that - even nitrite levels need to be near zero.
Sincerely Lasse
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