I always prefer to explain the background so the answer will make sense, to not only the questioner but others reading the thread who might be less knowledgeable than either of us. So don't mind what is already known.
Plants need 17 nutrients to photosynthesize (grow), and these come from several sources. The tap water at water changes add minerals, especially the "hard" minerals. Fish foods have all 17 nutrients but depending upon the number of fish, there may or may not be sufficient for the plants. Some nutrients occur naturally from biological processes; nitrogen (as ammonia/ammonium) and CO2 come from the breakdown of organics by bacteria in the substrate and from fish respiration.
We can supply nutrients to ensure none are missing, taking into account the above. However, aquatic plants have a fairly specific proportional need for nutrients, and if this is not matched trouble can result. For example, some nutrients in excess can cause other deficiencies within the plant, even if those deficient nutrients are actually present in the water. So it is important to keep things balanced.
This is where Flourish Comprehensive Supplement (Seachem) and FlorinMulti (Brightwell Aquatics) are so handy. For those with natural (low-tech) method planted tanks, these liquid supplements will provide all that is needed. However, they are intended to be supplements, adding to what is already naturally present, so depending upon the tap water GH and the fish load, some tweaking may be necessary.
To the two products mentioned. First, API LeafZone is, according to API, only iron and potassium. These may be the nutrients most likely missing in some situations, but without testing for everything this is difficult to say, although plant growth is a clue. One way to test this would be to acquire a small bottle of one of the afore-mentioned supplements and use it for 3-4 weeks. Observe the plant response. You will see if things improve. And BTW, both products are dosed in very small quantity, as they are concentrated, so they last a long time.
The GH of your water is critical, as the "hard minerals in the named products is minimal because they assume most have medium hard water. Just something else to be aware of.
As for the API CO2 Booster, I would never use this. This product, and the near-identical Flourish Excel (Seachem) is nothing but glutaraldehyde and water. Glutaraldehyde is a "hazardous substance" according to the Safety Data Sheet [http://cms.marsfishcare.com/files/ms...er_081810.pdf]
that is used in hospitals to sterilize utensils, in embalming fluid, in antifreeze, to disinfect the water bilges of ships, etc. It will kill some plants outright, and if overdosed can kill bacteria, plants and fish. It is as that sheet shows, hazardous to humans if inhaled or if splashed on your skin.
There is sufficient CO2 in a balanced aquarium to supply the needs of plants. The light must be balanced, and the other nutrients of course.
Hope this helps.