Change 50% of water, and your filter pads carbon and ammonia after a couple of days and its not clear you can change 50% of water should be clear after that. Pet stores sell drops that help clear water but is a temp fix only.
Have you changed your filter media? Usually changing the filter pack will help. Also you can change 10-20% of the water. If that does not help, there may be an algae film on the glass that can be cleaned as well.