Nitrite and nitrate (NO2/NO3,
mg L−1) was measured using Prodac (Aquarium products) test kits.
The total amount of ionized and unionized ammonia nitrogen
(TAN) was measured using an ammonia gas sensing combination
electrode (Thermo Orion, Model 95-12) connected to an ion analyzer
(Thermo Orion, EATM 920) according to