A marine aquarium requires high quality seawater, be it fish only or reef. A reef aquarium presents the highest demand but in any system it is irresponsible to allow quality to fall. One method of increasing seawater quality is by the use of chemical filtration: activated carbon and/or phosphate removal media. To be more accurate, phosphate removal is really a weapon against nuisance algae, but generally this algae is an indicator of lowered seawater quality.
Not everyone needs to use activated carbon or anti-phosphate media, I have never used either and count myself fortunate. There are ways of trying to ensure that chemical filtration is never needed. First, when mixing seawater is the tap water of good quality or should a reverse osmosis (RO) unit be used? Then there are regular partial seawater changes. Then there is the use of an efficient protein skimmer. Following this is the knowledge of the feeding demand and not overfeeding. Of course in the first place the aquarium should not be overstocked. Unfortunately there are those aquarists who do everything correctly but still have problems.
How should carbon be applied? This is easy if an external canister filter is in use as a layer of carbon can be placed inside. The carbon can be in granular form or in a manufactured carbon mat. If a canister filter is not in use then the easiest way is to obtain a small one. There are other ways, for instance a fluidised reactor, but the external filter is the easiest.
Activated carbon should be used over a limited period of time, the reason for this is that dissolved organic compounds (DOC’s) in the seawater are absorbed by the carbon. This means the carbon has a limited life span and as a guideline it should be changed every three weeks, check the manufacturer’s advice. The used carbon should be thrown away. Normal checks of the seawater should be made. Hopefully the activated carbon should demonstrate its usefulness.
Why is phosphate a problem? One of the indicators of lower than required seawater quality is the appearance of nuisance algae. Some algaes are welcome but not the stringy overgrowing or soggy mat stuff, usually green. Once this algae appears it can be slowly removed, one of the weapons is to remove a food source, phosphate.
Test the seawater. Phosphate is usually measured in parts per million (ppm) and a good reading is 0.03 or less. If the reading is 0.10ppm or higher then action needs to be taken. Phosphate removal media is usually in a small granular form and can also be used in a canister filter. It generally lasts longer than activated carbon. Because this media is smaller there is more likelihood that the seawater will create channels in the media reducing its effectiveness. This can be overcome by mixing the phosphate media and the activated carbon together. This obviously demands more space in the external filter, so if the filter is used for biological filtration it could be better to obtain another small external filter. Ensure that pads are placed before and after the media. Mix the activated carbon and phosphate media together in the amounts recommended by the manufacturer. The media should be changed when the one with the shorter life demands it, this is usually the carbon.
Testing should continue and, hopefully, improvements should be measured and seen. Patience is necessary as with most things in this hobby. If partial seawater changes continue, equipment such as the protein skimmer are maintained and feeding carefully done, plus the filter media is changed when required, then in time hopefully thumbs up!
(Photo: John Cunningham, part of aquarium)