Groundwater is used for evaporation, and water changes are performed at the rate of some 50 gallons per month. The last aquarium I saw during my stay in Holland was that of Mr. Hank van Stratan. This aquarium is 98 inches x 32 inches x 24 inches, with a volume of 320 gallons. Filtration consists of a trickle filter and skimmer. Water changes are performed using natural seawater at the rate of approximately 25 gallons per month.
Tap water is used for top-offs.
This aquarium also has live rock and the coralline algae growth is quite extensive. There are numerous hard and soft corals but not as many fish as in the aquariums shown to me by Leen Dekker. The most striking feature of this aquarium is the extensive growth of Xenia sp. In summary, the reef tanks I saw did nothing to dispel the notion that the Dutch have very nice aquariums. One of the striking differences between the aquariums I have seen in North America and those in Holland is the greater emphasis on soft corals than on hard corals-both in stores and in home aquariums.