When I first got my aquarium plants, they were a light green color. Then they started to lose their leaves.?

too much light is one possibility. They may be at the wrong temperature or [salt] or pH. The stems of some aquatic plants die naturally and then the remainder of the plant floats away and re-esatblishes itself in another portion of the lake. Anyway, you're plants are dead or dying and you can't reverse the process.

Many plants are grown out of water, emersed, before they a sold. When you move them into your tank (submerged), it shocks them, sometimes causing them to lose all their leaves. Some plants like crypto can take over 2 months to recover fully. When the leaves do grow back, though, they should look green (or whatever colour they are supposed to be) and healthy. It is likely not a problem of too much light. How much light do you have, though? Anything between .75 and 2 watts per gallon is fine for most low to mid light plants, and even if you have more than that it shouldn't a problem. If ever you do have high light issues, your plants will look tall and scraggly because they are growing rapidly towards the light, but not pulling enough nutrients from the water. Do you fertilize your plants? I use Flourish and Flourish Iron in my tanks; Flourish Iron is not always necessary, but plants like Crypto need iron to glow healthily. If you do not fertilize, I suggest you start. Don't follow the directions on the bottle (they are VERY generous, and you'll get algae growth). Rather, start with a little bit (a half-dose) every other week. You can increase until the plants look healthy or until you see minor algae formation, in which case, cut back a little bit. As for the iron, half-dose as well, and increase if required. Do you have CO2? If you do have light and lack CO2, you will get poor plant growth. Not all plants require CO2, mind you - "easy" plants like java fern, java moss, amazon sword, vallisneria, and pennywort, for example, do not need CO2. If you do want to go with CO2, the easiest, cheapest way is a DIY (Do-It-Yourself) reactor. What you'll need: 2L pop bottle Electric drill (or souldering iron) Airline tubing 2 cup Sugar 1 tsp Baking Yeast Warm Water A difuser Take the 2L coke bottle and rinse it. In the cap, drill a hole that is slightly smaller than the width of the airline tubing. Take the airline tubing and cut it an angle so it has a point; poke the point into the hole and pull it through with pliers or your hands. Inside the bottle put the sugar, and then fill it with warm water to about 2" below where the bottle starts to curve in towards the opening of the bottle; let it disolve, then add the yeast. Close the bottle. At the end of the airline, you'll need a diffuser, which puts the CO2 into the water. You can either just use a CO2 airstone, or you can buy a diffuser on E-bay. Or, if you have a canister filter, you can put the end of the airline into the filter intake and the bubbles will disolve on their way through the canister. Hopefully these suggestions will improve your plant situation :)

It's either not enough light, or not enough fertilizer/plant food. Since you're worried about too MUCH light, I'm guessing that plant food will fix you right up. Don't overdo it.