Here's The process I reccomend You do when you perform your weekly Water Changes.
STEP 1) : Draw out 1 Bucket full of tank water from your tank. (Either by using a syphon, jug whatever it takes to take out the water). So you will now have a bucket of water that has come from
your tank. You will need this for the next few steps.
STEP 2 : Remove the Filter media from the Filter itself, which I assume in your case is a series of Sponge cartridges, and place them into the dirty tank water that is in the bucket that you have just taken out of the tank.
STEP 3 : Now just dip them in the bucket of tank water and gently squeeze them, re-dip, re squeeze. Do this a couple of times.
STEP 4 : Now put the filter Media (sponges) back into your filter which is in the tank. DO NOT wash any of the filter media with tap water please.
STEP 5 : Throuw the dirty Tank Water away (down the drain) as you will
not put this back into the tank, Instead, fill up the bucket with clean tap water, TREAT IT with a dechlorinator such as Stress Coat or PRIME. These take anywhere from a couple of seconds to 5 minutes. A Rule of thumbs is allow 2 minutes to remove Chlorine and 5 mins for Chloramines.
STEP 6 : Add the newly treated water into the tank
Hope this helps. Do not worry as All of us, Including myself, have made mistakes or been "lost" in the beginning but you will get there, and constantly learn new things
