Well, here is the thing; The deterioration tells you that CO2 is marginal to poor. How you fix it depends on the sensitivity of the fish,economic factors as well as ergonomic and aesthetic factors. Everything stars with the light intensity. Instead of assuming, as you did earlier, that you needed to add more light, consider that it is the amount of light that is too high causing the problem. The first action you should take therefore is to REDUCE the amount of light. If you can accomplish this by disabling som bulbs then it will make your life a lot easier.
As I continually try to point out, Co2 is what grows plants. Have you ever sat under a gigantic English Oak and marvelled at it's incredible bulk and girth? Well all that bulk is mostly carbon. Light is an engine, the oven. Carbon is the dough that makes the bread.
If you are not able to disable bulbs or to raise the height of the fixtures, remove reflectors for the time being. Reduce the photoperiod. Reducing the light reduces the demand for carbon.
The next step is to change the flow configuration. It's clearly not working. I'm not sure why you have the holes pointed down. The preferred scheme for spraybars mounted on the aft wall is to have all holes and pumps pointed horizontally towards the front glss NOT pointed down.
Are you complying with the 10X rule?
Next is to think about supplementing using liquid carbon if affordable.
Last but not least is to consider an injection rate increase. This is the most dangerous, so make thes adjustments when you have time observe the fish for distress. You may need to drive the DC into the yellow. Is the timing of your gas correct? Is the bright green there before the light comes on? If not, you may need to turn the gas on earlier.
Do more water changes, an make sure they are massive. 90% is not out of the question, and make sure you do this at lights on, and that the plant leaves are exposed to air. That helps with CO2.
Clean the leaves during a water change. Rub them between your thumb and forefinger toclean away the slime and detritus. Every leaf...
Cheers,