112 GOLDFISH VAEIETIES AND 



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. 

 Mussels will usually clear green freshwater. The author tried a liberal 

 quantity of marine mussels to clear marine water, but three hours of direct 

 sun and five hours of strong diffused light multiplied the green vegetal 

 organisms faster than the mussels could keep pace with. The same 

 aquarium in the same light, when used as a regular goldfish container, 

 never became green. 



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 stand 

 the change successfully, 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, 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 evaporation will be inevita- 

 ble. No trouble will be experienced if the water is kept to a level, as sug- 

 gested, by the addition of freshwater. 



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

 tion should be given to the kind of carriers used. The action of saltwater 

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

 charging the water with poisonous metallic salts. Of the metals men- 



