MARINE AQUARIA 121 



wiped away, making a substantial, quick and neat result. The disad- 

 vantage of glass strips is that no thin glass is straight, the bend always 

 making an unsatisfactory job. Round rods are better in this respect. 



Lighting. Another radical difference from the freshwater aquarium 

 is that the marine aquarium requires considerably less light. When we 

 see such intense light at the shore, it is difficult to realize that only a few 

 feet down the light is so absorbed as to produce a very subdued effect ; 

 yet such is the case. If a moderately strong light is kept on marine water 

 it will quickly turn green. To clear it will take several weeks of standing 

 in the dark. Requiring only a weak light should, in many instances, prove 

 a strong recommendation for the keeping of a marine aquarium where one 

 has insufficient light for the successful development of freshwater plants. 



Strength of Marine Water. For some reason not understood, pure 

 ocean water is not as successful in the aquarium as that which has been 

 somewhat diluted. The reason may be that while the fishes can success- 

 fully withstand the change to weaker water, many of their microscopic 

 enemies are unable to do so — exactly the reverse of the theory of treating 

 freshwater fishes with a saltwater solution. Be the theory what it may, 

 experienced marine aquarists have obtained better results with diluted 

 water in still aquaria. Naturally, if new seawater can be continuously 

 pumped in, nothing could be better, particularly as this contains the 

 desirable small food otherwise difficult or impossible to supply. 



A hydrometer for testing the strength of salt in the aquarium water 

 should be provided. Natural seawater has a strength of 1.023 to 1.031. 

 If this is reduced to about 1.020, the animals will do better than at full 

 strength. It should not go below 1.017, nor above 1.022. 



Having established a certain water-level at a proper hydrometer 

 strength, it ought to be maintained at that point by the addition of pure 

 freshwater, never using marine water to make up for evaporation. The 

 salts do not evaporate, but concentrate, and soon the aquarium would be 

 in the lifeless condition of the Dead Sea or Salt Lake. A glass cover 

 will prevent some evaporation, but if an air pump is used, some evapora- 

 tion will be inevitable. No trouble will be experienced if the water is 

 kept to a level, as suggested, by the addition of freshwater. 



Shipping Seawater. If seawater must be shipped, careful consid- 

 eration should be given to the kind of carriers used. The action of salt- 

 water on zinc, copper, brass and iron is rapid, the resultant chemical 

 action charging the water with poisonous metallic salts. Of the metals 

 mentioned, iron is the least injurious and zinc the most, on account of the 

 rapidity of chemical action of salt on this metal. Galvanized iron is to 

 be avoided, as it is zinc-plated. The best metal in which to ship is tin. 

 This, or any other metal, should first receive a coating of asphaltum 



