The second fault was, strewing upon the surface of the sand a handful or
two of white powdered quartz, which, from having been pulverized in an
iron mortar, was so oxydized as to turn a deep yellow. This might have
poisoned the animalcula.

The first fault seemed to me the chief, but I proceeded to remedy both.
The whole contents of the tank being removed, it was thoroughly washed
on the inside, exposed for several days to the sun and air, and then
soaked for twelve hours in clean sea-water. This being thrown away, the
stones, scalded and well-washed, were restored, and clean sand, replaced
the old.

Water was drawn from the dock at high tide; but it was less clear now,
on the fourth of June, than that which had been got early in May. This
surprised me not a little; for, as I stood upon the wharf and looked
down into it just before sunset on the previous evening, I was struck
with its beautiful limpidity. Curious to see if its aspect remained
unaltered, I went to the same spot where I had stood the night before.
The tide was at the same height, but twelve hours had made a marvellous
change in the appearance of the water. Its sparkling clearness had given
way to greenness and turbidity, and no object could be seen a foot below
the surface. No storm had stirred its depths during the night,--why this
change? Conjecture was of no practical utility, and I returned home
satisfied that my fifteen gallons of water were as clear as any it was
then in my power to obtain. Covering the tub from the dust, I left it to
settle until sunset. Then the ever-useful siphon drew off two thirds of
it tolerably clear, leaving a thick green deposit upon the sides
and bottom of the vessel. Next day, it was again drawn off from the
sediment, (at this time, small in quantity,) and poured into the tank.
Several newly obtained plants of well-growing Enteromorpha and Corallina