MARINE AQUARIA 137 



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 de- 

 sirable 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 and brass is rapid, the resultant chemical action 

 charging the water with poisonous metallic salts. 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 

 varnish. Even galvanized iron when asphaltum-coated is safe for jour- 

 neys of moderate length, but the asphaltum will eventually chip off and 

 the pail or can should be carefully looked over each time before using. 

 It might be well to say here that the life of tin pails for any water will 

 last much longer if coated with asphaltum varnish. A thin coat spread 

 evenly lasts better than a thick one. 



The very best water-shipping medium is a protected glass bottle or 

 carboy. Arrangements can usually be made to rent or borrow a few of 



