Well, the first thing you need to do is pick an organism you like. A tank set up for a perch is very different than a tank set up for a pygmy sunfish. Size, current flow, amount of plants (and therefore substrate and lighting) would be different. Because you have a 25 gallon tank, you might want to avoid some of the larger species. No gar for you, sorry. The species you can comfortably keep involve: Darters, pygmy sunfish (Elassoma), killifish, livebeares, maybe some of the smaller sunfish species like the orange spotted sunfish, the smaller minnows, crayfish, madtoms, etc. Avoid bass, the larger sunfish species, gars, paddlefish, sturgeon, etc.; species that are large and need a lot of room.
Once you settle on a species, you can design the tank around it. Creatures that live in riffle environments like darters would enjoy a tank set up like this:
http://img.photobuck...um/IMG_5438.jpg It's got powerheads on one side and the intakes to the powerhead on the other side, to maximize current. You could still have a planted riffle tank, but the plants would be limited to the regions of the tank with lower current, such as the back and the surface. I kept darters in my planted aquarium with the plants in the background and the high current region up along the front glass. The picture in my profile is a female orange throat darter in Ceratophyllum demersum. She climbed up in the plants to better hunt her prey (swordtail fry).
Creatures that live in planted regions in the wild would enjoy something a bit more like the Walstad setup described in the book
Ecology of the Planted Aquarium by Diana Walstad. This involves a soil or kitty litter substrate, dense plantings of live aquarium plants, and only mild current instead of the churning current of the riffle tank. Here are examples of planted aquariums from the 2010 Aquatic Gardener's Association Aquascaping Contest:
http://showcase.aqua...ategory=0&vol=1Here's a picture of my 55 gallon Elassoma gilberti (gulf coast pygmy sunfish) tank from back when it was pretty:
http://gallery.nanfa...l size.jpg.htmlBut regardless of what kind of tank you choose, you need to establish a good pathway to break down the ammonia from fish food and waste. "Cycling" the tank refers to the nitrogen cycle, where ammonia is converted into less harmful nitrogen compounds. Here is some supplemental reading on fishless cycling, which you do by adding fish flakes to the tank every day as if you were feeding fish, but before the fish are added to the water.
http://www.fishkeepi...ing-article.htm The ammonia (toxic at even 1 part per million) is converted to nitrite by nitrosomonas bacteria, and then to nitrate (not toxic until 30 parts per million) by nitrospira bacteria. Plants also eat ammonium, as you can read about here:
http://www.theaquari...ical_FiltrationThese bacteria live on the surfaces of things, like the surface area of the sponge inside your filter. By placing a chunk of sponge from a filter that has been up and running for a while in your new filter, you can "seed" the bacteria there (provide the first few, from which your population will grow) and drastically reduce or even eliminate the time it takes to cycle your tank. You know that the tank is fully cycled when, after initially recording an ammonia concentration in ppm using a test kit, the ammonia and nitrite drops to 0 ppm and the nitrate is steadily increasing.
You'll want a new bulb for your light, by the way. It's best to replace bulbs every six months or so as they degrade. The one from 15 years ago is definitely no good. Look for a bulb with high lumen output and peaks in the red and blue regions of the spectrum. If it doesn't show you the spectrum on the side of the package, try for something that says "full spectrum" or "good for plants" or that has Kelvin value near 6,000 K.
Edited by EricaWieser, 05 July 2011 - 06:40 PM.