1.3.1 Introduction

Since it is our aim to culture rotifers without changing the water (recirculation system) it means that toxic compounds, built up by decomposition of uneaten food, dead rotifers and metabolic wastes will gradually affect the water quality.

The role of our biofilter will be to act as a pump and continuously transform toxic compounds of the N-cycle to less toxic compounds. In the N-cycle the following molecules have an important function in the nitrification process.

• NO₂^-
• NH₃
• NO₃^-
• NH₄⁺

The toxicity level of the different molecules for organisms may differ a lot. Especially the tolerance to NO₂ ^- and NH₄⁺ may differ a lot and some animals may be less tolerant to NH₄⁺ than to NO₂^- and vice versa. Besides the differences from species to species we also see differences from marine organisms to freshwater organisms.

The toxicity levels (in mg/l) for a few organisms
 

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