In marine aquariums, nitrate levels below 20 mg / l are recommended. In reef tanks (with stony corals) nitrate should not exceed 10 mg/ l. While LPS corals tend to tolerate somewhat higher values, SPS corals like lower values below 5 mg / l.
Here are 5 tips on how to lower the nitrate level in your reef tank:
#1 Regular water changes
Of course, with weekly partial water changes you reduce the amount of dissolved nutrients in the reef tank. It is also advisable to remove deposits from the substrate from time to time during water changes. Don't forget to clean your technical basin regularly and remove unattractive accumulations of debris. It is essential to use osmosis water for mixing salt water and for top-off, as nitrate levels in tap water may vary depending on the region you live. (In Germany the limit is 50 mg/l).
#2 Less feeding
Sure, your fish should not starve, but if you have too high nutrients, it would be worth considering reducing the amount of food. Generally, frozen food should be thoroughly rinsed. Prefer to feed several small portions (than one large meal) per day.
#3 Reduce fish density
Many fish = a lot of hungry fish = a lot of food = high nutrient load. A high fish stock, especially with active swimmers (which need a lot of energy) has a direct impact on water quality. One possibility is therefore to reduce the fish density (or to transfer them to a larger reef tank 😉).
#4 Get more consumers
Consumers, such as corals and macroalgae, take nutrients from the water to grow. Therefore, get more corals! Another consideration is to include an algae refugium in the sump. Use fast-growing species such as green algae for that.
#5 Filtration efficiency
Regularly clean mechanical filters such as fleece filters or filter socks and check the function of the skimmer and optimize if necessary. In that way waste products are removed at an early stage and contained nutrients do not even go into solution. Deni filters (nitrate filters or denitrification filters) can be purchased specifically for nitrate removal. These filters work in an anaerobic environment (without oxygen) to transfer nitrate via nitrite to nitrogen oxide by adding a carbon source.
#6 Carbon Dosing
The addition of carbon stimulates the growth of bacteria in your tank. Besides a source of carbon, bacteria also need phosphorus and nitrogen for their growth. Therefore they take up the phosphate and nitrate present in your aquarium water. Possible ways of adding carbon are the vodka method (cheap and effective) or the use of commercial products, such as Tropic Marin Elimi-Phos (safer to use). The addition of a carbon source can cause serious problems in case of overdosing. Before using the vodka method, you should therefore make sure that you know the details and dosage.
#7 Tropic Marin Reef-Actif
Reef Actif contains marine biopolymers of natural origin. Biopolymers are long-chain molecules that are able to bind other substances such as nutrients, pollutants or suspended solids. These substances are only released again after the biopolymers have been broken down. Since the polymers can be used almost exclusively by symbiotic bacteria in corals, sponges and other filters, the nutrients end up exactly where they are needed.
By the way: The exception proves the rule. There are also coral systems that are successfully operated with relatively high nutrient values. So always keep an eye on your corals - when they look happy and healthy, they are.