If you have the means and space to replace the 10 with a long 20, you would be far better off, because a 10 can support too few fish without constant water changes, meaning, no less than 70% weekly.

However, if you really have no choice and must use the 10, I would suggest at least 4 of the same species of small Cory cats. One of the cuter, smaller, yet easy to keep is the Panda.

Better, if you can find them, would be Pigmy cats, that won't grow over an inch long.

But no less than 4-5 of any Cory species, as they are miserable unless they can school.

Then, about 3 Octos, as even dwarf plecos need more than a 10.

If you really like Tiger Barbs, with no others but cats in the tank, they should do fine, but at least 6, to induce them to school and lessen interspecies aggression.

But no more than 6. Tigers may seem small, but just one has the total body mass of 3 Neon Tetras, and mass is the factor to consider, rather than length.

To maintain a 10 as even a mini community tank will require a far more powerful filter than usually sold with them. Don't use any rated for less than 30 gal.

You can combat algae and give the fish a healthier invironment with live plants in natural gravel. Do not use an underground filter with artifical plants, and do not expect any air driven UG filter to do the job, because they can't. Only a powerhead can really force a UG to work, and for a 10, it's not worth it.

A 30 gal. rated bio-wheel power filter will give you a much better a chance at success than any other filtration device I can imagine. It can even eliminate the need for an airstone and air pump, although a small, quiet pump that needs only to power a single airstone is still good.

One the tank is established, as long as you don't allow the bio wheel to dry out, you can and should, water change down to their dorsals every week, and the tank will maintain clear, sweet smelling, and healthy.

Good luck with your project.

I would stay away from the tiger barbs, there too nippy. Zebra danios for action and some swordtails and plattys for color. Overfeeding and too much light are prime causes for alge. Proper water changes and good filtration are also important.

I wouldn't go with the barbs in the 10G either. They need a little more room to swim back and forth. The 20L would do. I would assume the classroom has fluorescent lighting and is on for at least 8 hours daily. That combined with daylight from the windows will really be an algae problem in an unplanted tank (no live plants). Water Sprite is an easy fast growing plant, also anacharis. The plants will help by using up excess nutrients beore algae does. I would go with Fancy Male Guppies or Platys (same sex), about 5.

The aquarium is set up in its designated space, ready to go, so I don't want to even think of getting a larger one...tho' I appreciate and understand why that would be better.

I've written down the names of suggested fish and will check them out at the pet store. I'll pass on the tiger barbs. I've been reading about regular water changing, so I can do that. I'm looking forward to having a good-looking aquarium this year, and thanks to your help, maybe I will!

Oh, one other question...how about the fish called algae eaters? Do they really help control algae? Do they grow too big like plecos? Maybe that would be something I could get.

Thanks again.

Some algae eaters will eat algae in their juvenile (correct my spelling teach) stage, but usually stop as adults. They tend to get aggressive and some are classified as semi-aggressive (like the golden chinese algae eater). True Siamese Algae Eaters (SAE) don't get aggressive and are excellent algae eaters. In your sized tank only 1. Better then that for your tank are Otocinclus catfish (Oto's). They are tiny fish only getting about 3/4" at adult size and eat algae well. You could have about 5 with no trouble, they don't put alot on the bio-load.
With all this said the best way to control algae is to ID what type of algae it is. I would guess that green water and green spot algae are what you get (most common). Be careful not to over feed. Fish food contains phosphates, a nutrient to fish and also plants or algae (algae is just a primitive plant). Also, the ammonia that fish excrete is a form of nitogen or turns to nitrogen from the "cycle". When you add a ton of light from the windows and classroom lighting you are almost positive to get algae blooms. Keeping live plants will decrease nutrients as will frequent Partial Water Changes (PWC's). Diluting the water helps minimize nutrient build up (unless your water supply is the culprit, then thats a whole different ball of wax).
I would suggest a fishless cycle of your aquarium. have a link that explains the nitrogen cycle and has a link with in it to do a fishless cycle. The other option is using live plants.

Here is a link that might be useful: Nitrogen Cycle for beginners from the Krib

Do you have a heater for your tank? I just remembered you said last year you kept goldfish. If not put that on the list. Tropicals are a little more fragile to the nitrogen cycle then goldies (maybe because o the lower water temps)tats why I gave you the link above. If you are in NJ or eastern PA i'll donate some plants and fish to your class. I am moving and will be giving away the fish and plants until I settle in at my new home. I won't be able to set up tanks for a while when I move. I have a ton of Red Platy's and some of the Water Sprite I mentioned. The other plants need a little more room and/or lighting and other details. I just tossed about 5 gallons of plants over the weekend while doing maintainance on my neglected tank. I usually just ebay them, trade them or give them away. I just have had no time. Actually, I could mail the plants if you are far. I'll send them directly to your school. Let me know. You can just click my screen name to send an e-mail if I don't have a chance to check in for a while.

Socks, what grade do you teach? It would be great if you can involve the students in some of the decision making and maintenance of the tank. Maybe have them read a beginners book on fishkeeping and assist you with setup, etc. I always remembered what fish I had, if one died I'd replace it before my grandson noticed. Good luck.

Thank you all again for the helpful advice.

James, I'm not in a regular classroom setting. Our first, second and third grade classes come to the science room to do hands-on science activities, so I have a limited amount of time and a set curriculum with each group. Unfortunately, I don't have the time to spend as you suggested, but the kids often come in at recess to feed the fish and love to watch them. The kids are terrific observers. Thanks for the suggestion.

Be careful with the feedings, especially when establishing the nitrogen cycle. Less food = less poop = less ammonia. Algae concerns - Use the above "formula" and add -less ammonia = less nitrate production = less nutrients for algae to grow & less food = less phosphates = less nutrients for algae to grow

I got 4 zebras and 2 orange platys. The zebras are very happy and swimming around fast like they do, but the platys have been hiding in the plant for 2 days. I wonder if they think it would be like walking on the freeway to come out swim around where the zebras are.