No water changes in 7 months?!
YOU NEED TO:
A) To cycle:
Do a 50% WC 2x a week. Never change out the cartridge. Only swish it in old tank water every week or two. After a month or two you should be cycled. You can take a sample of water to your pet store and have them test it to confirm this.
Once your tank is cycled make sure to do at least a 25% water change EVERY WEEK. Buy a gravel vacuum
(usually less than $10) and use that. Your problem was that you never cleaned the water. The filter only helps - it doesnt do the work for you. It doesn't magically make all the waste matter dissapear. The filter doest even suck up all of the waste; only some of it. The water will have plenty of dissolved stuff in it. Thats why it needs to be cleaned out.
Here's a demonstrational vid that show how to do a water change using a gravel vac. Ignore the part about needing salt & filter cartridges as you dont need that.