ClearFox® nature has received the license for retrofitting with a bio stage according to DIN EN 12566 part 6 from the Deutsches Institut für Bautechnik (DIBt) as only small sewage treatment plant without energy requirement.

If a suitable pre-treatment (e.g. three chamber septic tank) exists, it can be used as pre-chamber, if it has passed the leak test. Instead of installing a complete ClearFox® nature, a ClearFox® nature bioreactor can be retrofitted in this case. The cleaning performance corresponds at least to that of a complete plant.