My plants aren't doing well?

Freshwater, 65 gallon, 2.5 years old.



My substrate was well formulated in the beginning for plants. I have a bio Eheim filter of 5 levels, greater than that of the aquarium. Nitrates are always a bit high even with weekly 30% changes. PH at around 6 and stable. GH much lower but stable.



I have a back drop to my aquarium which has grown a fine (beautiful) grass, moss algae but also likes to grown on plants.



Have noticed that algae dominates plants. Most older plants are dying off.



Liquid CO2 lowers the PH in my aquarium so I do not use it every day.



I have replaced plants which should all be tollerable to 28-30% temps F.



I have discus fish as main fish.



Time for a complete overhaul? How long does original substrate last to maintain healthy plants?



suggestions?



ThanksMy plants aren't doing well?
You need quick growing plants that will use the nutrients quicker than the algae.