There’s more to the chemistry of a marine tank than salt and water. Chris Sergeant explains some of the key marine components.
WHEN IT COMES to marine water quality and chemistry, it’s best to start
simple and focus on the parameters you will already be familiar with. In freshwater aquariums, for example, the most important piece of equipment is the filter, where nitrifying bacteria facilitate the conversion of harmful ammonia into nitrite and then nitrate.
In a marine tank, this is where your live rock comes in. As well as its aesthetic function, and its slow-release source of calcium carbonate, the porous nature of live rock means it plays host to the aerobic and anaerobic bacteria needed for biological filtration to occur. The resulting product of the nitrogen cycle, nitrate, is harmless to fish in low quantities, but acts as fertiliser for the likes of zooxanthellae algae that reside within photosynthetic coral tissues.
Nitrate
Coral reefs are naturally low in nutrients, so while detectable levels are needed for a healthy reef, if nitrate content creeps past an acceptable level, this abundance of food spurs on algae growth, and with a boost in zooxanthellae, your previously colourful corals will adopt a dull shade of brown instead. Not only that, but elevated nitrate (and phosphate) levels increase nuisance algae that can overgrow corals.
The natural reaction is to reduce the nitrates and starve the algae, but what this actually does is put those that depend on it into direct competition, and more often, it will be the undesirable algae, along with cyanobacteria or dinoflagellates that survive at the expense of the corals. Water changes and a reduction/refinement in feeding regimes help reduce levels, as does dosing an organic source of carbon to encourage bacterial growth within the live rock. You could also add a refugium to the sump that will then encourage macro-algae to naturally consume the nitrates, which can then be harvested periodically from the system.
While fish-only tanks tolerate higher nitrates than those that support corals, a very general rule of thumb would be to aim for a nitrate reading of <5ppm, but there are plenty of examples of thriving reefs with levels far exceeding this.
Temperature
Temperature is straightforward in an aquarium scenario, with a narrow range of 26-28°C being ideal. In the wild, temperatures will vary with location and depth, and in parts of the Red Sea, they comfortably exceed 30°C, although this is not somet
