
CONDITIONS OF LIGHT, ETC. 

The odor of the water is also a means of determining its condition, as 
when this is strong, vitiation has advanced to a dangerous degree, and to 
keep the inmates alive it is not only necessary to entirely refill the aquarium 
but it should be cleaned, the plants reset, and after a few days the water 
again changed. Experienced aquariists can tell the condition of the water 
by its taste. 
When the conditions are good there is no need of changing the water 
for long periods, as filling in what has evaporated is sufficient, or remov- 
ing a part of the lower depth and adding a little fresh water, from time to 
time, especially when the weather has became warmer. 
The aquarium should have a considerable change of water, more than 
half, when hot weather sets in, and it may be advisable to change part of 
the water occasionally, say once a month, if not perfectly clear. The new 
water also brings into the aquarium some of the mineral salts necessary 
for the plants and animals, which may become exhausted by long standing. 
Culturists of the food fishes recognize the benefit of occasionally turbid 
water, as the precipitation of the particles of soil act as a disinfectant, and 
the mineral substances are required by the fishes to digest their food. In 
ponds and streams, rainstorms will supply this requirement, but at the 
beginning of the feeding period of the alevin, breeders of the trout and 
other food fishes make the water of indoor hatching basins thoroughly 
turbid twice a day by pouring into it a mixture of water and rich sod soil, 
after which the young fishes take their food with particular readiness. 
The breeder of the goldfish supplies the required mineral constituents by 
placing dishes of turf in the rearing tanks, which is especially necessary to 
furnish soil artificially in wooden tanks and cement basins, as otherwise 
the health and growth of the fishes will be impaired. Muddy water is a 
favorable remedy for some of the illnesses of goldfishes and is frequently 
used. A small piece of plaster of paris is also beneficial, as it furnishes 
lime to the animal inmates. 
Dr. W. Koch demonstrated that the addition of like quantities of 
nitrate of ammonia and biphosphate of potassium with a minute quantity 
of iron to calciferous wellwater, in which a number of water plants were 
placed, soon produced very green and turbid water rich in plant life 
consisting principally of alge, voucheria and wolfha, when kept at a 
temperature of 50° to 54° F. ‘This admixture produced conditions favor- 
able to the development of the ever present spores of these low plant 
forms, which are beneficial to the animals in the aquarium, 
When much animal life is present in proportion to the size of the 
aquarium and the plant growth is insufficient, frequent changes of water 
are necessary. In overstocked aquaria this must be done daily, but 
176 
