You need to find the balance between light and nutrients that will provide what the plants require in which case algae is discouraged. This takes some explaining.
Light involves the intensity (brightness) and the spectrum. Light is what drives photosynthesis in plants, and each plant species has a minimum requirement for light intensity. Duration does not make up for any deficiency in intensity. Once you have the intensity, then the duration can be used to provide sufficient time for the plants in balance with the available nutrients, but not beyond so algae will then take advantage.
Plants photosynthesize according to what botanists term the law of minimum. This means that if the light is sufficient and nutrients are available, plants can use these and photosynthesis full out, up to the point when any one factor is no longer sufficient. So it is the minimum, not the maximum, that determines the plant's response (growth via photosynthesis).
If the light intensity here is adequate for the plants, and if all 17 nutrients are available to the plants, then you can use duration to control algae. But changing thee duration will have no effect on algae if the light is not sufficient intensity for the plants, or if nutrients are out of balance.
I know it sounds complicated, but it really is not once you grasp the fundamentals.
Something about your split lighting period...don't do this. It is bad on fish. Light is important for fish, as much as for plants. Light drives the inner biological clock known as the circadian rhythm. When you divide the photoperiod, it cause serious consequences for fish. Every 24 hour period must have the "daylight" (= tank lighting here) as one consistent period, and a period of total and complete darkness for several hours. The time between these two, what would replicate dawn and dusk in nature, can be almost anything. It is the duration of the daylight and the total darkness that is important for fish.
Plants need this too, but they are able to take advantages unlike fish can do. The reason the split time is sometimes suggested to control algae is because the CO2 builds up during darkness and is used when the tank lights are on (daylight to the plants). By splitting the photoperiod the CO2 has a chance to rebuild. But as I said above, this is very damaging to fish, and there are better methods to deal with this.
We need to know the specs on the light. From the photo I am assuming it is LED, and my experience with LED is non-existent. But others may be able to advise once we know. Also, what if any fertilizers (plant additives) are you using? What is the GH of the water? And what is the fish load? All of these are sources of nutrients for plants so all must be factored in to the solution.
I did, after your amazing response buy a fluval pressurized co2 kit and install (I was told I didn't need this), I have the flourish tabs near all the plants but I also bought the micro nutrients and added to the water today to help. I really hope this works!!! Thank you so very much!!!
