What am i doing wrong here

Hello guys i am a amateur hobbyist need your ideas and advice about my tank .i had this tank for 3 years now .Its cycled and the bacterias are very much present and active all the life inside the tank seems to be fine except the plants there is no growth the stem plants there are no leaves in the bottom,the java ferns have holes and some of them are blackening and melting.i have steady DIY co2 system,finding difficult to maintain clear waters and i dont know what to buy for water parameters test kit (strips or liquid kit)this is my planted tank specs: 1.100L tank 2ft tank length 1ft height 30 2.sunsun 602b canister filter 3.DIY co2 injected 4.flora lumios Q40 MODEL 20W 5 hours on 5.Weekly fertilized Am i burning them or is it due to deficiency?need your opinion