Name the plants that you have. You mentioned that you use tab fertilizers. These are good for plants that are root heavy in terms of gaining it's resources. Maybe some of your plants prefer liquid ferts.
Is that a reverse flow undergravel filter I see? If so, that's your problem. Plants have a heck of a time getting established when their roots are being flooded with rushing water 24/7. With plants sitting there decaying like that you can't help but have algae problems.
Nope. I don't have an undergravel filter. Those outlets coming up from the base of the tank are the outlets from the canister filters underneath the tank.
I am getting the impression I should just pull all the plants. They are in bad shape.