How to Keep a Salt- Mater Aquarium 125 
Then buy two specific gravity balls'; one, the clear glass bulb, 
floats on the surface of the water; the green one sinks. A small 
glass or zinc syringe will also be wanted. Every morning the 
water must be well syringed ; if the green bulb begins to rise to 
the surface this means that evaporation has taken place—that the 
water is too salt, its specific gravity is greater. To remedy this, 
add very slowly a syringe-full of rain, distilled or boiled water 
until the green bulb sinks. If too much water be added the white 
bulb will begin to sink. 
After a few days add one specimen of the sea-weed which you 
wish to observe. If a red seaweed, it is best to select a plant 
growing on a rock or shell, or if this cannot be found, chip off a 
piece of rock, with the plant attached, with a hammer and chisel. 
It may happen that one wants to keep a seaweed washed up by the 
sea, which has been torn from its attachment; in this case tie it to 
a stone with silk and insert it carefully amongst the other stones. 
It is well, if possible, to avoid seaweeds which are very rapid growers; 
those plants which grow naturally below low water mark are the 
easiest to cultivate. 
When the first plant is properly established more may be added. 
The great thing to remember is, that nothing must be allowed 
to decay in the aquarium. Dead sand-hoppers and shrimps must 
be carefully removed with forceps, or the experiment will end in 
failure. 
Another point is: do not change the water. The same sea¬ 
water will last for years, if its specific gravity is kept right by 
adding fresh water to compensate for evaporation, At the most ? 
draw off the water once a year with a syphon and re-fill with fresh 
sea-water. 
The aquarium must not be kept in the sun, though a little 
sunshine occasionally is of advantage. The periwinkles will eat off 
the green spores, which settle on the glass, especially in sunlight, 
and will also help generally to keep the water sweet. Their 
number must be regulated according to experience; enough must 
be kept to keep the green spores in check. 
How to germinate red sea-weed spores. Plant a healthy female 
plant of red sea-weed (I have tried several species of Polysiphonia 
successfully). It is very important to be quite sure that one’s 
plants are correctly identified and it is also well to get to know the 
1 These can be obtained at Negretti & Zainbta’s, 38, Holborn 
Viaduct, E.C. 
