Dinoflagellates are probably one of the most persistent pests in marine aquariums. The single-celled creatures make themselves noticeable in your aquarium in the form of unsightly brownish deposits. At first they only spread on the substrate, but become more intense during the lighting phase until they finally overgrow the entire reef structure. For you, this means: act quickly and keep at it! Dinoflagellates are extremely adaptable and it takes a lot of patience to get rid of them in the long term.

Below we give you important tips on how to declare war on the dinosaurs.

#1 Combating the causes of dinoflagellates

The cause is always a so-called biological imbalance. But what does that mean in detail? Dinoflagellates often appear during the running-in phase. Since they are among the first settlers, they are happy about free settlement substrate - free here means: free of competitors such as bacteria or higher algae. Dinoflagellates are extremely adaptable and can compensate very well for fluctuations in salinity or nutrient content. This gives them a huge advantage over less adaptable species and they prevail over a long period of time. Dinoflagellates often grow after cyano blooms or major cleaning of the aquarium decorations. Treatment with medication disrupts the tank biology, rigorous cleaning of the decorations by the aquarist leads to free settlement substrate again. Since dinoflagellates are always present (be it in the form of plankton or as zooxanthellae in corals), they always have a chance to multiply unhindered. Bacterial preparations can help prevent this. The use of higher algae such as Chaetomorpha or Caulerpa can also prevent the spread of unwanted pests. Light, flow and filtration should also be optimized. Finally, don't forget the water values. A well-staffed bottom cleaning crew consisting of snails, hermit crabs and gobies can also help prevent the spread of dinoflagellates.

The spread of dinoflagellates typically begins on the substrate. The brown deposits become more visible as the day progresses. Photo: anonymous

#2 Curb the proliferation of dinoflagellates

Growing dinoflagellates depend on vitamins, amino acids and trace elements (especially iron). So for the time being, do not add such substances. Continue to skip the weekly water changes. Even with fresh salt water, you are adding a lot of trace elements to your aquarium. If you do want to suck out some of the deposits, collect the water in a bucket and let it run over filter cotton first. This way you can easily pour the "old" water back in.

#3 Starve dinoflagellates

Dinoflagellates also feed on bacteria and diatoms. Diatoms depend on silicate. If you remove silicate from your water, for example using a silicate filter, you are also depriving the dinoflagellates of their food source. You should also avoid adding bacteria or bacterial food (carbon sources).

Some dinoflagellate species also depend on light to feed on, similar to plants. A gradual reduction in the lighting duration to a maximum of 6 hours (for the sake of your corals) will therefore have a positive effect on the decline in the number of dinos.

#4 Lime water against dinoflagellates

If you add lime water to your aquarium, you increase the pH value. A high pH value always means low CO ₂ values. CO ₂ in turn promotes the spread of dinoflagellates, which carry out photosynthesis. Therefore, set your pH value as high as possible (max. up to 8.5), whereby the value should never rise by more than 0.1 per day. It is best to slowly add the lime water in the morning before switching on the lighting. Lime water is highly alkaline - avoid direct contact of the solution with your reef inhabitants and allow the lime water to drip into the technical tank, for example.

Alternatively or additionally, you can also run the intake air of the skimmer through soda lime ( _CO2 filter) to increase the pH value.

#5 Supportive measures

Some dinoflagellate species are toxic. To prevent poisoning, especially from algae eaters such as sea urchins, gobies, snails and hermit crabs, additionally filter your aquarium water using activated carbon to remove any poisons that may be produced.

Some dinoflagellates are poisonous and can be fatal, especially for algae eaters such as snails, sea urchins or hermit crabs. Photo: anonymous

#6 Lights off, UV on!

In the case of a severe infestation and a dinoflagellate plague that becomes more noticeable and stronger over the course of the day, we recommend that you turn off the light completely for 3 days. If necessary, even cover your aquarium to prevent sunlight from entering. During this dark phase, the dinoflagellates, which are usually bound to the substrate, enter a planktic stage and are now free in the water column. The dinoflagellates can be effectively removed in this way using a powerful UV filter.

#7 The last resort: the chemical weapon

Commercially available solutions for dinoflagellate infestation are available from many retailers. You should strictly adhere to the manufacturer's instructions. The solutions are added at night and should be combined with a reduced lighting phase during the day. It is best to remove adsorbent materials/filters (activated carbon, phosphate/silicate adsorbers, zeolite...) from your aquarium, as they absorb the active ingredient and inhibit its effect. The treatment period is at least 2 weeks and should be continued for at least 2 more treatments after the deposits have disappeared to be on the safe side. The agents are generally compatible with fish, corals and other invertebrates. The exception is sea urchins, which should be moved before treatment if possible.

We hope that these tips will help you keep your dinoflagellates under control and that you will soon be able to enjoy your aquarium to the fullest (dinoflagellate-free). The most important thing is to react early and keep at it!