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Re: Need some expert help with water experiment at elementary school


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.

The best solution to your heat problem is to partially bury the tank in the ground. All you need is a few hours with one of the little bobcat frontloaders to do it. Since you are working with a school you may be able to find someone or some company that would be willing to donate some time to help you set up your equipment. Also, some ferns around the perimeter would help to provide some shade.

For electrical power, you could also go overhead. Many electric utilities will plant a few poles for a school for free (our local one will). Then you need a run of triplex from the building to a receptacle or subpanel that can be mounted near your pond area. You could also span the cable between light poles if there is a parking lot nearby. You should *not* use extension cords, indoor NM cable, or outdoor UF cable for this application. None of those cables is suitable for the stress involved with aerial suspension and will break over time. Again, this is an area where you may be able to get some donated time and/or materials from a local utility or electrical contractor. Many companies like doing the occasional "community outreach" project, especially if you can provide them with some kind of recognition for their donated services.

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.

Typical natural ponds don't have any powered circulation. Most natural small ponds also do *not* have any fish in them, but rather a wealth of microscopic and small critters (daphnia, rotifers, etc...). If you put any fish in you will lose most of the smaller life like the daphnia since the fish will be quick to clean your pond of them.

If you have to put in some fish you will probably need some kind of circulation. There are outdoor battery-operated air pumps intended for use in remote research sites. (try the link I list later)

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?

Depends on the metal. Galvanized (zinc-dipped) tanks are commonly used in agriculture and don't seem to be a problem. I don't think the zinc comes off fast enough to built to toxic levels in the water. If you want to be on the safe side though, you can get a polyethylene tank liner from someplace like http://www.aquaticeco.com/ (Aquatic Ecosystems, which has a lot of large tank stuff since they support the agriculture and fish-farming industries).

adds cooling in winter. The temperature swing will be substantial. Goldfish
can handle it, is there anything else?

All the normal pond critters can handle it, but many burrow into the silt on the bottom to winter so you might need to consider that. I'm not sure about the fish.

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.

Your normal seasonal changes will take care of the life cycle for you. If you can get a few gallons of natural pond water from a REAL pond (not one in someone's backyard that is constantly treated trying to make the water clear), about 2/3 water and 1/3 silt from a shallow area, you can get a decent pond starter culture. If you want to pick certain parts of certain life cycles for certain species you're going to need power so that you can maintain your pond conditions at some specific point. If you're on a tight budget you'll probably need to let the pond's natural cycle determine what you study and when you can study it.

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
pond?

I don't think you could mimic thawing glaciers in a pond of the size you're talking about. Most natural ponds are many tens of thousands of gallons, and they don't have much of a freeze-thaw cycle to watch. You're going to be limited with what you can do in terms of mimicing natural systems in your pond. I think you will have the best results filling the tank with your local water, making sure it is dechlorinated, which if you don't have chloramine can be accomplished by just letting the tank sit for a while preferably with some aeration. Then put in several gallons of pond culture from a natural pond, and make sure to get some duckweed. The more starter culture the better. Your tank should start looking like a natural pond within a few months, and the pond critters are fairly durable and easy to maintain. Lots of science classrooms around here have "pond tanks" that were started in just this way, and require zero maintenance except for the occasional water level top-off.

-Bill


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Waveform Technology
UNIX Systems Administrator