Hi and welcome to the forum
Algae grows anywhere there is light and water. Add some nutrients from fish food and waste, and the aquarium is a perfect place for algae.
The best way to control algae is to reduce light and nutrients, and have live plants in the tank. You got rid of the live plants so there is nothing left but algae to use the light and nutrients.
If you have no plants in the tank, you only need a dim light on the tank in the evening when you are home. If you have bright lights from when you had plants before, reduce the intensity and amount of time the light is on.
Or add some live plants. Floating plants like Water Sprite (Ceratopteris thalictroides/ cornuta) will use light and nutrients and shade the tank so algae will have a tough time growing. Other floating plants can also be used and you don't have to fertilise them or use CO2.
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Do bigger water changes and gravel clean the substrate to reduce nutrients in the water. If you only do a 25% water change once every two weeks, you will have a build up of nutrients. You would be better off doing a 50-75% water change every week or every two weeks. Make sure you gravel clean the substrate whenever you do a water change.
Make sure any new water is free of chlorine/ chloramine before you add it to the aquarium.
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You shouldn't change the filter media/ materials unless they are breaking down (falling apart). The filter media holds colonies of beneficial bacteria that convert ammonia into nitrite, and nitrite into nitrate. You get rid of nitrate by doing water changes. If you replace the filter media, you get rid of this good bacteria and you get ammonia build up in the water. Ammonia is a great food for algae but poisonous to aquatic organisms.
You clean sponges and other types of filter media by squeezing or washing them in a bucket of aquarium water. When the media is clean, you re-use the media in the filter, and tip the bucket of dirty water on the lawn/ garden outside.
You can add sponge to most power filters and sponge will last for years. Just buy a sponge that is slightly bigger than the filter pads/ cartridges and use a pair of scissors to cut the sponge to fit. I used AquaClear sponges but there are other brands and they all work as well as each other.
If you are going to add sponges to a filter, try to add the sponge and leave the other filter media in place for 2 months. Then remove the old filter pad and put more sponge in its place. If you can't add sponge while all the original filter media is in the filter, remove 1 piece of old media and put a sponge in its place. Let the filter run for 2 months and then swap another piece of old media for sponge and let it run for 2 months. Then swap out any other media you don't want.
You can buy cylindrical sponges with a hole through the centre. These are used in some brands of internal power filter. You can use these sponges on the intake strainer of most external power filters where they act as a prefilter and supplement the filter media in the actual filter.
