7 ways to control dinoflagellate algae in reef tanks

Dinoflagellates are probably one of the most persistent pests in the reef hobby. The unicellular organisms will form unattractive brownish coatings in your reef tank. At first they only spread on the substrate, but become more intense during the lighting phase until they finally overgrow the entire reef scape. 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 run.

In the following we give you some important tips on how to fight the dinoflagellates.

#1 To fight the cause of dinoflagellates

The cause is always a so-called biological imbalance. But what does that mean in detail? Dinoflagellates often appear during the beginning of a tank cycle. As they are among the first colonisers, they are happy to have a free substrate to settle on - free here means free of competitors such as bacteria or macro 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. Dinoflagellate growth often occurs after cyano blooms or major cleaning of aquarium decorations. Treatments with medication upset the tank biology, rigorous cleaning of the decoration 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 unchecked. To prevent this, bacterial preparations can help. The use of higher algae such as Chaetomorpha or Caulerpa can also prevent the spread of unwanted pests. Furthermore, light, flow and filtration should also be optimised. Finally, the water values should not be forgotten. A well-staffed bottom cleaning crew consisting of snails, hermits and gobies can also help prevent the spread of dinoflagellates.

Spreading of dinoflagellates usually starts on the sand bottom. The brown coatings usually appear thicker during the day. photo: anonymous

#2 Stop the proliferation of dinoflagellates

Growing dinoflagellates depend on vitamins, amino acids and trace elements (especially iron). Therefore, refrain from adding such substances for the time being. Continue to skip the weekly water changes. Even with fresh salt water you add a lot of trace elements to your aquarium. If you do want to remove some of the deposits by siphoning, collect the water in a bucket and run it through filter floss beforehand. This way you can easily tip back the "old" water.

#3 Starve out dinoflagellates

Dinoflagellates also feed on bacteria and diatoms. Diatoms depend on silicate. If you remove silicate from your water, e.g. with the help of a silicate filter, you also remove the food basis for the dinoflagellates. In addition, you should refrain from adding bacteria or bacterial food (carbon sources).

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

#4 Kalkwasser against dinoflagellates

If you add Kalkwasser to your aquarium, you will increase the pH value. A high pH value always means low CO2 values. CO2 in turn promotes the spread of dinoflagellates, which carry out photosynthesis. Therefore, set your pH as high as possible (max. up to 8.5), whereby the value should never increase by more than 0.1 per day. It is best to add the Kalkwasser slowly in the morning before you start the lighting. Kalkwasser is highly alkaline - avoid direct contact of the solution with your reef inhabitants and let the Kalkwasser drip into the sump, for example.

Alternatively, or in addition, you can also run the intake air of the skimmer over soda lime (CO2 filter) to raise the pH value.

#5 Supporting measures

Some dinoflagellate species are toxic. To prevent poisoning, especially of algae eaters such as sea urchins, algae blennies, snails and hermits, filter your aquarium water additionally through activated carbon to remove any toxins that develop.

Some dinoflagellates can be toxic and may lead to the death of algae grazers such as snails, sea urchins and hermit crabs. Photo: anonymous

#6 Lights off, UV on!

In case of heavy infestation and a dinoflagellate plague that becomes clearer and stronger during the course of the day, we recommend that you switch off the light completely for 3 days. If necessary, even cover your aquarium to avoid incoming sunlight. During this dark phase, the dinoflagellates, which are usually substrate-bound, enter a planktonic stage and are now free in the water column. With a powerful UV filter, the dinoflagellates can be effectively removed in this way.

#7 The last resort: the chemical attack

Commercially available solutions against dinoflagellate infestations are available from many retailers. You should strictly follow 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 adsorbing materials/filters (activated carbon, phosphate/silicate adsorbers, zeolite...) from your aquarium, as they absorb the active substance and inhibit a corresponding effect. The treatment period is at least 2 weeks and should be continued for at least 2 more treatments after the deposits have disappeared, just 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 to keep your dinoflagellates under control and that you will soon be able to enjoy your aquarium again to the full (dinoflagellate-free). The most important thing is to react early and keep at it!