You don't need a CO2 system, people just have them to increase the growth of the plants in their tanks. For a 38 gallon tank, I would get two 2 liter soda bottles and fill it up with 2 cups of sugar, 1 liter of warm water, 1 teaspoon of baking soda, 1/4 teaspoon of yeast.
1. Mix the sugar with the water.
2. Put some of the sugar water in a small cup and add the yeast, but don't stir yet.
3.5. Put the sugar water in the 2 liter bottle.
3. Wait 15 minutes and stir the yeast in the cup.
4. Wait 15 minutes after stirring to put the yeast mixture before adding it to the bottle.
5. Add the baking soda and fill with more warm water until it gets up to the curvature point near the top of the bottle.
6. Swirl the mixture in the bottle to make sure everything is well mixed.