Sand, fine gravel, or coarse gravel?
I am a big fan of small (fine) gravel or coarse sand. Food particles easily slip between the cracks in large gravel, where they rot, out of reach of most fish. In the tanks with finer gravel, the food sits on top of the substrate so that bottom-feeders can pick it up later and munch. Chicken grit and pool filter sand are great sources of cheap gravel for large tanks. Chicken grit is usually made locally, and may have minerals or shells that will increase the pH and hardness of water. Pool filter sand is my favorite - it has a very regular particle size and doesn't harm the barbels of my catfish. The only Corydoras sp. with great looking barbels in my house are on catfish who live in tanks with pool filter sand.
If you use an undergravel filter, you will be limited in the size of gravel you can use. If it's too fine, it will slip between the holes in the filter plate and clog it up (some people put a layer of open cell foam between the filter plate and the gravel to prevent this, but the foam can clog from fish waste, so you need to vacuum the gravel regularly). If it's too coarse, you will not have much surface area for your nitrifying bacteria. Also, consider running your undergravel filter in reverse. To do this, buy a powerhead that sucks water in and pushes it down the tubes into the gravel, instead of the other way around. By doing this, you force water up through the gravel, not down into it. This may help keep the gravel and filter plate from becoming clogged with fish waste and goo.
One other note: do you need gravel? Most people think tanks look more natural with gravel. Many fish breeders choose to use no gravel - it makes the tank easier to clean (no nooks and crannies for uneaten food and fish waste to collect in), and it does have a certain appeal - you can see your fish reflected in the glass below. Just think about it. Some fish love gravel and will feel insecure without it. Choosing the right gravel requires knowing a bit about your fish.
Colored or natural?
Think about this one. When I set up my first tank, I bought red and blue gravel. I thought it would look nice with my orange and black goldfish. Now I'm stuck with the hideous stuff forever. Which do you want to catch your eye, the gravel or the fish? Look at tank in pet stores and books. Which tanks grab you - tanks with bright gravel, plastic plants and underwater bubbling scuba divers, or tanks with tan/brown "natural" gravel, some driftwood and green plants? To each their own, but make the decision carefully and think - "natural" goes with everything. :-) Do make sure that the gravel you buy doesn't contain any minerals or shells that will increase the pH or hardness of the water, unless that is what you want. Gravel with crushed coral, shells or some kinds of rock will do this. To test it, you can drop a few drops of vinegar or other acid onto the gravel. If it fizzes, it will probably increase the pH of neutral water. You can also leave two cups of water on the counter for a few days - one with just water, one with gravel and water. Test the pH of both to see whether the gravel changes anything.
Rinsing your new substrate
No matter what kind of substrate you get, make sure to rinse it well before adding it to a tank. To rinse new gravel, put about a gallon of gravel in a 5 gallon bucket, and run cool water into it. Stir and mix the gravel well with your hands, until the water is cloudy and silty. Pour the water out carefully, being careful not to lose your gravel. Refill bucket and repeat. This is easy to do outside with a garden hose, or in the bathtub. When the water is no longer silty or cloudy, drain the gravel, pour it into another bucket or into your new tank, and start again. Rinsing gravel is tedious, but it will greatly improve the clarity of your water.
When you add water to the tank, put a bowl or plate on the gravel, and pour your water into that - this way you won't disturb the layer of gravel in the tank and stir up more particles. If the water is cloudy, just let the filter run for a few hours and it will probably clear up.
After many years of struggling with algae, I have come to peace with it. Like weeds in your garden or lawn, it's all a matter of definition. Certain types of algae are quite beautiful, like the furry/hairy algae in our tank at work. Some are harmful to fish, smother plants and look awful, like blue-green algae (cyanobacteria). Cyanobacteria can be treated with antibiotics, but this may harm the bacteria in your filter and add to the problem. If your algae is due to overfeeding, the best way to fix it is to do lots of partial water changes, vacuum the gravel, and keep the filter freely moving.
Photographing Fish Clean the outside glass carefully.
Diluted vinegar does a great job getting the salty scaly drips off of glass, but be cafeul not to get it in the water - fish don't like it one bit, trust me. Exercise extra caution with any spray glass cleaner (like Windex). Spray it into a paper towel or cloth many feet away from the tank. Ammonia is a common ingredient in glass cleaner, and we all know how toxic that is to fish! If you use a flash, any little droplet or dust on the glass will stand out because it has been illuminated so well. Sometimes autofocus cameras will try to focus on the glass instead of the inhabitants, especially if the surface is dirty.
Clean the inside of the glass.
Even if you don't see a lot of algae, you will have a clearer picture if you scrub or scrape the front glass. I find that old credit cards are perfect for cleaning glass - they don't scratch the surface and seem to take much less "elbow grease" than sponges.
Use the brightest light source possible.
Flashes work well, but sometimes they misrepresent the true colors of the fish. They can also have a limited range and can emphasize imperfections in the glass. They can give the scene a harsh look. If you do use a flash, take pictures at an angle, not "straight ahead". That way, your flash will be reflected off to the side, not back into the camera. Try putting a bright light off to an angle, shining into or onto the tank. Any reflection you see will be in the final picture, so don't take pictures naked! Sometimes you will be able to see the photographer and the camera reflected in the glass. I have a halogen light on a stand that I have tried using for pictures. With this light, I can aim it down into the tank and get nice pictures without using the flash.
Borrow or buy a digital camera. This seems silly, but trust me - at least borrow one to practice. Instant feedback speeds up your learning, and you can experiment freely when pictures are free. I only keep about 10% of the pictures I take - fish are difficult subjects. If I photographed our fish using a film camera, I'd have to get a second job to pay for film and development.
Try putting the fish in a "show tank". Many of the snazzy "perfect looking" shots you see in slide shows and magazines are actually taken in show tanks. These tanks are set up just for pictures. Try using a spare 5 or 10 gallon tank.. buy a little gravel, put in a few rocks and plants, etc. You don't need a filter or anything. Acclimate the fish carefully. You may need to give it a day to adjust to the water (use old tank water from its original tank, if that water is clear). Then you can take a picture in this "perfect" tank. Some people even put a plate of glass in the tank, separating the fish from the surroundings! Imagine putting a plate of glass in the tank so that the front had a 1-2" gap - just big enough for your fish to move its pectoral fins.. the fish would be forced to stay in the foreground. This has to be done carefully so that the fish isn't harmed, of course.