112 GOLDFISH VARIETIES 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 wsed. 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- 
