Sterilisation of seawater

Especially for the cultivation of sensitive phytoplankton species such as Isochrysis or Rhodomonas, the salt water used should be sterilised in advance.

We use the chemical sodium hypochlorite for this purpose. This is contained in chlorinated cleaning agents, for example, which you can easily buy in the supermarket. When buying, please make sure that it does not contain any surfactants or other additives. The branded product DanKlorix©, for example, contains no additives other than sodium hypochlorite and can therefore be used without hesitation. Caution: We strongly recommend that you wear gloves and safety goggles when handling such chemicals or cleaners! You should also make sure that the room you are working in is well ventilated. And please remember to protect your clothing, as chlorine is a very effective bleaching agent and causes unsightly stains when it comes into contact with coloured textiles.

Depending on the contamination of the source water, you should use between 0.5 and 5 ml of chlorine cleaner per litre of salt water. We ourselves usually add 0.75 to 1 ml of chlorine cleaner to our medium, as the (germ) contamination of tap water in Germany is very low and it is best to use osmosis water for preparing the salt water anyway. We always add fertiliser to the salt water after sterilisation with sodium hypochlorite so that vitamins, for example, are not oxidatively damaged. Theoretically, sterilisation of the medium is complete after around 30 minutes. However, it is advisable to leave the preparation for 12 hours or preferably overnight.

Before the phytoplankton fertiliser and the starter culture can be added, the chlorine must be completely neutralised. This is where Antichlor comes into play. Add one ml of the antichlorine solution for every ml of chlorine cleaner previously used.

4 hours after the addition of antichlorine, all chlorine should have been converted to harmless hydrogen sulphate. This can be easily checked with chlorine test strips. If you don't have chlorine test strips to hand, you can also use your nose - it is very sensitive to chlorine.