photosynthesis notes - Biology Junction
If your intention is to grow only low to medium light plants, I have found only liquid products such as Flourish Excel or NilocG Enhance to be necessary (basically to help the plants out compete the algae for CO2/carbon available via natural process), or the use of combining Alkaline and Acid buffers to the water which will then produce CO2.
Usually, nothing more need be added in a healthy aquarium eco-system for these plant types. To be clear, you can definitely get higher growth in a "high tech" aquarium, and there are certainly some hobbyists who enjoy tinkering with their system. But, if you are a beginner and wishing to keep it simple, then the low tech approach is for you.
C4 photosynthesis: how some plants avoid photorespiration
This is an often misunderstood aspect of aquarium plant keeping.
There is so much anecdotal information that is out of date with more current aquarium/plant biochemistry information. Not only do plants need many of the minerals found in GH, but, just as important, potentially dangerous upward pH swings can occur if your GH is much below 50 ppm during peak plant photosynthesis.
For example, I observed a pH of 6.8 in the morning and then a pH of 7.4 in the afternoon in a tank where GH was low or almost non-existent.
Another way to utilize NilocG Enhance Seachem Flourish Excel for bioavailable carbon (CO2) in a better, staggered way, rather than all at once, is a calibrated drip system.
In this experiment I was able to get 20 drops per minute. I measured 20 drops and this was equal to a ¼ tsp. So 4 minutes would equal 1 tsp. There are 6 tsp in one fluid ounce. So at this rate you will go through a ounce in 24 minutes. Add the correct dosage for your aquarium size then add the water (RO or DI water is best to mix with Flourish).
Example: For a 50 gallon planted aquarium you would add one capful (5 mL) of Flourish Excel (or 5 mL of NilocG Enhance). Then, depending upon how long you would like to stagger the drip would determine the amount of water. For this example I would suggest 20 oz. of water to mix for 8 hours of drip (24 minutes per ounce x 20 ounces water/Flourish Excel solution).
With larger containers, longer dosing times can be achieved.
However, even though Flourish Excel or Enhance can remain active for 24 hours, from my experience I would suggest 8 hours for best results (keeping in mind that CO2 is not utilized by plants after dark as they use oxygen instead during non-photosynthetic periods).