If you want to cycle your tank you need your filter to be on all the time. If you only leave it on during the day time you might as well not use it. This means you should have been doing two weekly water changes a week - one 50% and one 100%. This is why he has the rot.
At this point, he is not fit to use to cycle your tank, which can take up to 2 months. This guide talks about how to do it without hurting your fish, but you need a reliable drops kit for ammonia, nitrite and nitrate: http://www.bettafish.com/showthread.php?t=47838
At this point, You should be doing at least 50% change every other day with 100% weekly. Personally, I would do 50% daily with 100% weekly. In addition to this I would use an actual antibiotic. I'm not sure what's available in your area..
Salt should be measured and not pinched - 1 tsp per gallon predissolved for fin rot. A pinch would have not been enough to help with anything. However it can only be used up to 10 days so it needs to be discontinued at this point, and you can try it again correctly in another couple weeks if you need to.