Have the the plants you photographed been in the tank for one full year?
I assume since you are talking daily/every other day excel you don't dose CO2, correct?
What type of lighting are you using?
I have a 75 gallon, with well water that has a pH of 8.5, GH of 14, kH of 11. You didn't mention your pH but I would bet it's like mine.I used that water initially, but wasn't happy with how things looked. Fortunately I have a RO system used for my reef tank, and drinking water, so I went to mixing 50% well water with 50% RO for water changes.
The ferts I dose are flourish, fl iron, and fl potassium twice weekly, and fl phosphate once weekly. My nitrates run 10ppm, so i don't add N either.
I found my PO4 levels was reading zero on my test kit, which is why I added the fl PO4, and did notice within one week or so of starting to dose it that the new growth looked much healthier, and was not prone to the BGA the original leaves had. Again the tank was only setup 3 months, so that may have been coincidental, as the tank was still maturing.
Instead of excel I chose to dose CO2. When I found swings between pH values of 7.0 when running CO2 (one bubble per second) during lighted hours, and 7.6 when not dosing at night I added a ph meter/controller to be able to add CO2 while maintaining a steady pH of 7.0.
The first two months after setup my plants looked exactly like yours, but new growth starting coming out looking good about 3 months or so after initial setup.
If you have moderately high lighting (PARs over 50) I would suggest adding CO2.
The brown 'algae' I had was taken care of within one week after adding the algae crew (SAEs, otos and nerite snails). Again, that may have been due to the timing of a new tank as well. Had a little bearded algae on my driftwood that has all but faded away.
In my case the improvement in health and growth of the plants I think was due to the combination of getting lower pH and hardness values from the RO/well water mix, adding CO2 while maintaining a steady pH, and probably nature - time to allow the tank to mature more.
Sounds like you have yet to hit the magic point with the ferts, lighting and carbon in your tank.
Looking back on it finding a "balance" point for good plant growth in a freshwater community tank (without algae) I found to be more challenging than getting a balance in my reef tank (also 75 gallon) and growing hard corals.. Go figure!
I am sure others with much more knowledge can chime in with more specific advice.