So, your initial experiment already used different liquids (plain water and a sodium bicarbonate, baking soda, solution). I think you had more (faster) results with the bicarbonate, so you will probably want to add the same amount of…
moreSo, your initial experiment already used different liquids (plain water and a sodium bicarbonate, baking soda, solution). I think you had more (faster) results with the bicarbonate, so you will probably want to add the same amount of bicarbonate to whatever solution you use for your follow up expt.
For different colored lights, you want to be sure that the intensity (brightness) is the same for each of the colors used. A start is to use the same wattage of lamp, but even here different colored lamps, of the same wattage, will produces different amounts of energy. If someone has a light meter, that would be great, you just need the same amount of light. If they are not the same at the start, move one lamp closer (to increase) or farther (to decrease) until they both are the same. If no one has a meter, see if your parents or someone at school has an old manual, single-lens reflex camera with a built in meter. Again, all you need is the same intensity.
Different liquids are going to have the same problem - - anything pigmented will absorb light differently. So, if water is your control, don't use Coke, use a clear soda of some kind instead - -or dissolve something else in water besides the bicarbonate - e.g, salt or sugar.
Light duration is probably the most straight forward. Just be sure that when your different treatments are in the light, they are right next to each other so all other environmental conditions are identical.
Good luck