Coral - March/April 2010

change has been dramatic. Within four days of starting ozone treatment, the water became a light blue. It does not take much ozone to break down water-coloring compounds. We have been measuring for dissolved organic carbon (DOC) for several months now. Using the Hach UV254 method in conjunction with a spectrophotometer, in less than two months we have seen a gradual and steady decrease in DOC levels from a high of 2. 4 ppm to less than 1. 2 ppm. The levels continue to drop and our goal is to bring the exhibit more in line with natural reef levels at less than 0.6 ppm.

Increasing the oxidation-reduction potential (ORP) in the exhibit has proceeded very slowly. At present we are still working to balance ozone injection into both protein skimmers and to increase the ozone injection rate to the optimum amount. Since the system is also supplying ozone to several other exhibits that are slowly being brought on line, it is currently only running 8 hours a day and not on weekends. Once ozone is on 24 hours a day, the exhibit ORP will likely begin to increase; it is currently 280 mV.

Calcium and alkalinity levels have remained within
normal ranges: above 400 mg/L calcium and above 3.0
meq/L for alkalinity. These levels are a reflection of the
large amount of concrete used in the construction of
the system, which is probably leaching calcium and car-
bonates. There are also six Schuran calcium reactors but
these have been offline for the most part; when they are
not running we do not see much of a drop in calcium
or alkalinity. Magnesium levels were consistently below
1,200 mg/L; we recently boosted this to 1,320 mg/L.

BIOLOAD CONSEQUENCES

With more than 2,000 fish and hundreds of corals—not to mention four daily feedings of flake food, pellet food, frozen mysis, Cyclop-eez, prawns, Mazuri gel diet etc.—it should be no surprise that nutrient levels have increased. Nitrate (NO3) levels have slowly climbed since we first started stocking the exhibit in May of 2008 and now are at about 12 ppm—not too bad and presently not a major concern.

Orthophosphate (PO4) levels are, however, another story since they have slowly climbed from a low of less than 0.05 ppm to a current level of 0.21 ppm. A daily addition of a calcium hydroxide slurry has helped to slow this trend but other measures need to be implemented—a granular ferric oxide (GFO) reactor along with activated carbon will most likely be installed in the near future.

It is also likely that lanthanum chloride will be used to bring the level down as low as possible before the GFO is brought online.

In the next issue we will take a look at how an exhibit of this size was stocked with fish and corals over a period of four months.

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