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Need some expert help with water experiment at elementary school

I am setting up a science garden at a local elementary school and as part of
this garden I plan to put in a pond. The purpose of the garden is to study
plants, water, and adaptation. It will have a pond and a meadow and a
raised, sandy desert area, all in a 75' x 25' area. Kids will study biomes,
parts of plants, plant and animal adaptations, pollination, various bugs. I
will be there each week to monitor and conduct whatever experiments or
maintenence is necessary. The gate will be locked but is in the playground
so the kids will be able to see it but not touch it unless with the teacher
or me.

It will be entirely funded by the PTS -- very low budget! I have located a
metal horse watering stock tank, 5' diameter and 2' tall and plan to bring
it to the garden, it will be entirely above ground, with a gravel path
around it. Almost immediately as the year begins, the 5th grade will study
water and then plants. My plan is to fill the tank up and use the
microscopes to see how the water is changing day to day or week to week.
There is no real shade, a thin Savanah Holly 10 feet to the north. I intend
to have a flimsy wire fence added around the pond to keep vandals from
accessing the drain and taking the pond for a roll around the playground.
That short fence will grow vines to shade the metal walls of the pond, but
initially I think we will have a heat problem for temps are near 100 degrees
currently. There is no electricty available, I cannot go under the concrete
surrounding to bring it from the building. There is an automatic watering
system and the school district has installed a short fence to help keep the
basketballs out of the area.

My question is, can this even work? 300 gallons, no shade, no filtration, no
circulation (though I have considered a solar powered fountain, $80, I fear
that vandals will take it or add bubble bath to the pond.) My thought is to
fill the pond with water, then watch it turn green, then add water lilies
and/or other plants and some fish. As this school is very near a wild area
full of West Nile mosquitos, I cannot wait long to add fish, or else I'll
have to add mosquito dunks.

Is a metal tank going to add harmful things to the water? I recall it as a
bit greasy, what should I wash it with? Vinegar? Is the metal going to leach
anything harmful? I know it will rust some after several years, at least on
the rim, is that a problem?

Can I add daphnia and actually see them clear the pond, that would be cool!
Should I cover the pond with netting to keep mosquitoes out, or just add
fish? Which fish? Goldfish are so destructive, mosquito fish are so
prolific. Any cheap tropicals I should consider? Would gouramies or bettas
do well? Would tadpoles eat mosquito larvae fast enough? Water temp could
get quite high initially with no natural shade, certainly in excess of 85,
and winter temps in my pond of the same size get to near 40 degrees, some
winters a tiny bit of ice on the surface even, but I have a fountain which
adds cooling in winter. The temperature swing will be substantial. Goldfish
can handle it, is there anything else?

I can see two fates for this pond, first, it could be drained each summer
and renewed each fall to study the same "beginings of life" cycle each
year -- most likely. Or, if this is pain to manage, it might be filled with
dirt to become a bog, to study adaptation of plants.

I would love to have some help to manage this as an exhibit on how life
begins in water and have it follow as natural a cycle as possible. As water
flows from a glacier to a lake, what happens to it? Can I mimic that in this

Tap water in my area is 8.2 pH, GH 10 and KH 9 degrees. I suppose this
neighborhood is similar, but it is very far from me so I don't know for
sure. We get 55 inches of rain a year, in great bursts on one or more
inches, then dry, so on occasion the water pH could vary dramatically.