JAMES W. ATZ 



MATERIALS SUITABLE FOR SEA- WATER SYSTEMS 



Any discussion of water as an environ- 

 ment, artificial as well as natural, ought 

 at least to mention the attributes that in- 

 timately connect this unique substance 

 with life, namely its great specific heat, 

 latent heats of fusion and evaporation, 

 and thermal conductivity, its high surface 

 tension and dielectric constant, its trans- 

 parency, and its tremendous solvent power 

 combined with chemical stability. These 

 characteristics were first penetratingly 

 analyzed by Henderson (1913), and they 

 have been reviewed by Sverdrup, Johnson, 

 and Fleming (1942). Of them, only 

 water's close approach to being the uni- 

 versal solvent presents any special prob- 

 lems in aquarium management. 



Because of water's ability to dissolve 

 a wide variety of toxic substances and 

 because of the extreme sensitivity of most 

 aquatic animals to them, the only certain 

 way to keep water suitable for most ma- 

 rine life is to use chemically inert ma- 

 terials throughout the water system. 

 Copper is a good example of a problem 

 material. This heavy metal is acutely 

 toxic to fresh-water fish in concentrations 

 of a few parts per hundred million, but in 

 hard alkaline waters its toxicity is con- 

 siderably reduced (Doudoroff and Katz, 

 1953). In sea water, as might therefore 

 be expected, copper is somewhat less toxic, 

 and at the New York Aquarium and the 

 .Tolni G. Shedd Aquarium, prophylactic 

 doses of 0.20 to 0.25 p.p.m. (parts per mil- 

 lion) are considered safe for the great 

 majority of marine fishes (Carleton Ray, 

 personal communication; Braker, 1961). 

 At the Steinhart Aquarium, however, a 

 number of marine fishes have been found 

 to be sensitive to concentrations of less 

 than 0.20 p.p.m. (Herald et al., 1962). 



Invertebrates are much more sensitive; 

 for example, sea-urchin larvae were 

 strongly affected by 0.03 p.p.m. of copper 



(Wilson and Armstrong, 1961). Surpris- 

 ingly little metallic copper need be exposed 

 to sea water to produce a dangerous con- 

 centration of dissolved copper. Braker 

 (1961) placed two U.S. pennies in a sys- 

 tem containing 6 gallons of sea water with 

 1 gallon per hour flowing over the copper 

 coins. He found a concentration of 0.1 

 p.p.m. of copper in the ambient sea water 

 at the end of 12 hours, and 0.58 p.p.m. at 

 the end of 48. (At this rate, it would 

 take more than 5 years for the coins to 

 dissolve.) "We have received several re- 

 ports that fresh sea water flowing through 

 a single copper, brass, or bronze fixture 

 can pick up enough copper to kill larvae. 

 One reason for the acute sensitivity of 

 fishes and aquatic invertebrates to a heavy 

 metal under these conditions is that they 

 act as biological accumulators, removing 

 the metal from solution and retaining it. 

 Few determinations of the toxicity of 

 substances in sea water have been made, 

 but materials toxic in fresh water are 

 usually also toxic in sea water, although 

 somewhat less so. Exceptions are known. 

 Boetius (1960) found that although mer- 

 curic chloride is less toxic to small fish in 

 sea water than it is in fresh, phenylmer- 

 curic acetate is more toxic in sea water. 

 Certain aquarium cements, whose per- 

 formance in fresh water is satisfactory, 

 break down in salt water and release sub- 

 stances that kill fish. In general, all met- 

 als should be avoided, even those like lead 

 and stainless steel that are sometimes con- 

 sidered safe. Wood and other question- 

 able materials may be covered with several 

 coats of a good grade of black asphaltum 

 varnish, but this protective coating will 

 not last indefinitely and requires periodic 

 checking. Cement is inert, but only after 

 it has been "cured," a process that may 

 take months. Chemically ideal for sea- 

 water systems is hard rubber, also called 



