fertiliser
 

is it safe to add a plant fertiliser to my aquarium with fish as some of my plants seem to be dying.

yes just read the instructions- you are diluting the chemical, always best to add it to a prepared barrel of water before adding to tank- make it part of your water change routine.

oh ok thanks im going to buy some soon , is there any certain ones which are better

i use sera florena-
what you need to look for is iron and magnesium ferts.

would i need to remove the carbon in my filter

dude carbon should only ever be used to remove chemicals- ie treatments for disease, else yuour wasting your money.

the carbon just comes with my tank because iv got a juwel filter with loads of different filter media inside it.

sponges are the next best thing to using nothing- i would recommend you have atleast one layer of siporax in there, and at teh very least remove the carbon and the white wool.

whats siporax