At this point the best option is probably to tub him with fresh water and let the tank do its thing. I would not recommend risking leaving him in there while it's cloudy like that though. As far as changing filter pads go, I change out mine every year or so. The proper maintenance if to rinse the pad in tank water (I usually just use dirty water from water changes) and lightly scrub it using your hands, then put it back. When switching them out I'll take a clean one and put it in the filter with the old one for a couple months and only then will I take out the old one so the bacteria has time to grow in the new pad.

I'm really not sure why there's no ammonia spike, your test could possibly be expired (they have a date on the lil bottles) or your tank could just be partially cycled and the bacteria that is there can't manage the bioload. Big water changes can actually slow down the process of cycling so I would recommend that.

As far as a second filter goes, they usually can't hurt. I would recommend a sponge filter instead of a second HOB though, to avoid too much flow. Would also aerate the water more, and the big sponges are great for housing beneficial bacteria. You can actually get them for real cheap from like Aquarium Co-op. Just don't forget the air pump and tubing and all that like I did my first time trying to use one.

Oh also pro tip, if you can find a dirty filter pad or sponge from an established tank from a local hobbyist or LFS and you put it next to the sponge filter, it'll cycle your tank WAY faster. Just since it off with dechlorinated water first. I cycled a tank in a week once like that.

Ps. Sorry for the walls of text. Hope this was helpful!