Question
Hi! I am a middle school student and I go to a Magnet school. I am doing my first big science project. My experiment is about how different oxygenating plants effect a guppy's size (in length). They're all going to be males, and all of them are going to be babies. I just need to ask a few questions to help me carry out this experiment. I'm going to put each guppy and plant in an half-gallon tank. Please mention any flaws that I have do in this experiment.
1. Do I need to install a filter?
2. How can I measure the fishes length without harming them?
3. Is they're any tips I'll need to grow the following plants; hair grass, water violets, elodea crispa, and water milfoil? If so, please list them.
4. Please recommend any good websites i could do research on.
Try to summit your answers before October 29. I will really appreciate your help.
Celista

Answer
1.  You need 1/2 lb of gravel at the bottom of each tank.  You also need an air stone in each.  You can use one or two air pumps and split to as many stones as you have tanks.

2.  You can put a ruler up to the front of the tank and take a photograph or two.  Then look at a good photograph and decide the what the measurement appears to be.

3.  The air stones I suggested would slow the plant growth.  You could just keep an eye out for ammonia by testing regularly.  A pH test kit might be a good idea to get too.  Those are the two things that can stunt fish growth and harm fish with the least warning.  If either of those two parameters goes off track, perform a 50% water change and dechlorinate the water if from the tap.  It shouldn't have a long term effect on the oxygen levels.  I would buy a fairly powerful light and use a decent reflector.  You could place 1/2 a fertilizer tablet under each plant at the beginning of the experiment.

4.  http://fish.mongabay.com/plant_care.htm