The light-dependent reactions begin in photosystem II.

NADPH and the hydrogen ions made in the light reactions are used to split a phosphate off of each (putting phosphates back to make more ATP) and to provide the energy and hydrogen to turn the remaining chemical into glyceraldehyde phospate, also called phosphoglyceraldehyde, or PGAL.

The Light-Dependent Reactions of Photosynthesis

This reaction occurs in two sections, which we'll call light reactions and dark reactions.

Introducing: Photosynthesis (The Light Reactions)

It is also noteworthy that in acidic environments phosphate ions react with Iron and make iron less soluble and thus less available. Therefore if one require more iron, slightly alkaline values are more desirable.
Reference:

What Kind of Reaction Is Photosynthesis? | Sciencing

*GH (general hardness): 100 ppm or sometimes higher; this is more important than many realize for planted aquariums.
“During photosynthesis, a rise in pH can occur in water with low alkalinity (20 to 50 mg/L) or in water with moderate to high bicarbonate alkalinity (75 to 200 mg/L) that has less than 25 mg/L hardness”.


Photosynthesis (Light Reactions) - YouTube

The “watts-per-gallon" formula was based on the older T8 & T12 fluorescent lights, many of which were not of optimum PAR/Kelvin and especially PUR, and are severely lacking in the area of lumens per watt. Besides that, "useful light energy" (aka PUR) is something that is often overlooked and is an area where the new generations of LED lights that emit "natural daylight" spectrums cannot be beat.
That being said, along with Metal Halide, the new generation SHO and T5s are also relatively strong in this area. Lumen focus and restrike is an area in which the LED and metal halides reign supreme with almost all light energy directed where the light needs to be: in your aquarium.

Light Reaction of Photosynthesis Essay - 616 Words

The beginning aquarist is likely to think that if there's enough light to see then it's enough for plants to grow.
However, that's not true. If you want to grow healthy plants, and not just algae, you need enough light for them to use for photosynthesis and create energy.
It used to be that people advised 3-4 watts per gallon as a VERY basic principle. But, due to modern lighting technology this is now considered an outdated notion (with PAR now more the norm).

Photosynthesis light dependent reactions - SlideShare

Often many "hands-on" advanced aquarium keepers will utilize the most advanced pressurized CO2 system (as well as complicated fertilizer delivery). While this might be the way to go for certain high end hobbyists, from my experience (as well as other experienced pros) the expense of time and money these methods require are not always justified if all you desire is a nice but basic planted aquarium.
In fact, as a generalization, just utilizing good lighting, filtration, and basic fertilizers, as well as simple, natural CO2 generation methods (e.g. fish respiration, buffers, and plant material decomposition) can still produce good results. Albeit not to the level of advanced methods (think Walstad Method or German method)!
This of course is not to knock advanced methods for those who want optimal plant growth.

Light reaction in photosynthesis SameeraYusuf

Gasses such as oxygen and CO2 are added and subtracted from the aquarium via surface agitation.
Generally speaking it is oxygen that is added and CO2 that is subtracted. In nature, CO2 is organically added via fish respiration or other biological activity along with decomposition and chemical reactions such as alkaline buffers upon acids in the water.

Light Reactions | Photosynthesis | Chlorophyll

Before I seem to be over-hyping the relatively new SHO technology, there are other excellent planted aquarium light choices as well.

The new generation T-2 lamps and fixtures are also great for plants. With over 70+ lumens per watt, lower wasted light energy (less wasted than SHO & other CFLs) and very compact size, the T-2s have a lot going for them.
For example two 13 Watt 6400 K T2s are excellent for a 20 gallon with plants that require high light. Multiple T2s can be interconnected for larger aquariums so as to require just one outlet.
For instance, you could have four 13 Watt 6400K T2s for a 60 gallon with plants requiring medium light.

I should also note that there are also many excellent T5 fixtures available for planted freshwater aquariums, although T5 technology is not quite as good as T2 in lumens per watt (they are based on slightly older technology). The T5 is still vastly superior to most available T8 and T12 lights still available.