Don't dose your tank with an algicide, they are often toxic to fish even when dosed according to the directions.
You need to do more water changes. If your nitrAtes were at a desirable level, you wouldn't have the extra nutrients for the algae to grow, and you would no longer have an algae problem.
If you can't afford the salt, then perhaps you need to re-evaluate the fish you choose to keep. Algae is an indicator of an underlying problem in the system, and until you fix that underlying problem (too many nutrients in the water) then you will continue to have this problem. Also, high nitrAte levels for extended periods of time can cause stress, disease and also death in the majority of all aquatic life (except for plants, they love it!)