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Tanks for Marine Aquaria . 
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simplest arrangements usually prove the best; and it is advisable to avoid the 
use of cement, if, by any possibility, the intended design can be carried into 
effect without it. Blocks of water-worn stone and old serpulse and oyster 
shells can be easily worked up into picturesque rockeries without the aid of 
cement ; and it is equally easy to provide places of concealment for creatures 
that love to hide, by merely lodging a flat stone or large shell in such a 
position as will allow the creatures to enjoy the shelter and still remain within 
view. If, however, cement must be used, let it be the best Portland, mixed 
with two or three times its bulk of sand. As it hardens quickly, but a small 
quantity should be mixed at one time. It is a bad plan to construct an 
elaborate rockery in a tank, for we do not know how soon we may wish it 
away, and find that in this particular case it is less easy to destroy than to 
construct. It is better to construct the affair in separate blocks, which will fit 
together in the tank without being made fixtures. Empty flower-pots form 
good centres for blocks of rock-work, affording strength and a firm base 
without weight. Common coke washed with cement to alter its colour is an 
excellent material for small rockeries, being extremely light and manageable. 
All cemented work should be steeped in fresh water in the open air for at 
least a fortnight before being consigned to its final place in the aquarium. 
K 
