First off, adding salt will feed the algae not kill it. Stop adding cycle to your tank secondly.
Algae is not always a bad thing. It is good to have some algae which shows the tank is healthy. Before you start dumping chemicals into your tank, understand how algae works and what you can do to control it.
Algae are mostly-photosynthetic organisms that sometimes resemble plants but are not plants, having no true roots, stems or leaves. Algae grow in freshwater and saltwater. Saltwater algae are sometimes referred to as "seaweed." Like plants, algae require light and nutrients to grow. We supply plenty of both in our aquariums, with several hours of aquarium lighting a day and nutrients like nitrates and phosphates from fish waste.
Algae come in many forms. There are microscopic, one-celled algae, filamentous algae that resemble hair, algae that grow in sheets, and macroalgae that look like plants. There are even algae that live inside the outer integument ("skin") or calcium shell of some corals, anemones, and other sessile invertebrates called zooxanthellae. There are slimy-looking algae that are often not algae at all, but a colony of primitive photosynthetic organisms known as cyanobacteria. There are also very hard-to-remove little dots of green that sometimes grow on aquarium panels which also are not algae, but diatom or radiolarian colonies (microscopic, one-celled, animals with hard shells) with algae incorporated in their matrix. With all that said, let us answer some common questions right up front:
Algae growth is inevitable in an aquarium.
Algae consume nutrients in the aquarium that if allowed to accumulate, are harmful to fish. Algae can be a good thing.
The presence of green algae in an aquarium indicates a healthy environment for fish.
There is absolutely no way to completely prevent algae from growing in an aquarium, without killing the other life in the tank.
Chemicals should never be used to control the growth of true algae in an aquarium, and should only be used in rare circumstances to control cyanobacteria.
Correcting a severe algae problem requires time and patience.
Natural methods of controlling algae are the best and most effective.
Algae removal from the tank panels can be done on an as-needed basis, but no more than once a week. Removing algae involves either correcting negative water conditions to control or slow excessive algae growth, or an age-old process known as "elbow grease" (scrubbing it off!). Algae removal in an aquarium should be done only when necessary. We have seen many aquariums where daily removal of algae resulted in fish that were so stressed, most had diseases and were dying. You should never remove all of the algae from your tank. Allowing some algae to grow in the aquarium can be beneficial to the aquatic environment. When algae is removed from aquarium side panels, care should be taken to select an algae scrubber that will not hurt the finish of an aquarium. Be careful not to get gravel caught in an algae scrubbing pad where it can scratch the aquarium. Never use household cleaning pads to remove algae. They contain fungicides that kill fish.
First, test the water you are filling up your tank with. Many public water supplies (our homes) have a concentration of nitrates at around 7ppm or higher. (Bottled water is no better).
This could be the start of your problem.
Be sure your tank is not within direct or indirect lighting such as a window or in a room where the lights are on constantly. Is you tank near a heat source. Sometimes we do not take into consideration a fishtank is near a heat register which can and does add additional temperature changes to your tank.
Did you clean the filter as well? Be sure the entire filter is cleaned and free of algae.
Use a razor or scraper and gently scrape all sides of your tank. Clean your gravel and return it to the tank as well. DO NOT wash the gravel in the tank. The residues of the algae will remain.
If you have a stick on thermometer, get yourself a floating one. The stick on thermometers pick up ambient air temperatures from OUTSIDE the tank and can be up to 10 degrees off. DON"T trust them. Try keeping your tank at 72 for a couple of days.
You can also purchase phosphorus pads for around $2.00 at your local pet store. These can be cut to fit with your filter and remove large amounts of phosphorus. These can be reused over and over just remember to rinse them out well when you clean your tank.
Test your water. If you find your water quality is all your tank isn't near a heat or light source, ok but still getting algae turn the temperature down or off and let it run. (Saying you don't have fish that is) You will want to scrape the sides of the tank and do a water change no more than 20% every other day. This should only be done if the algae returns in a heavy form.
If you need any more help, you can im or email me.